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Fundamentals of Information Technology

This book is a part of the course by Jaipur National University, Jaipur.This book contains the course content for Fundamentals of Information Technology..

JNU, JaipurFirst Edition 2013

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Index

ContentI. ...................................................................... II

List of FiguresII. ........................................................ VII

List of TablesIII. ........................................................VIII

AbbreviationsIV. .........................................................IX

ApplicationV. ............................................................. 129

BibliographyVI. ......................................................... 135

Self Assessment VII. Answers ................................... 138

Book at a Glance

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Contents

Chapter I ....................................................................................................................................................... 1Number System and Codes ......................................................................................................................... 1Aim ................................................................................................................................................................ 1Objectives ...................................................................................................................................................... 1Learning outcome .......................................................................................................................................... 11.1 Introduction .............................................................................................................................................. 21.2 Binary System .......................................................................................................................................... 2 1.2.1 Binary to Decimal Conversion ................................................................................................ 41.3 Decimal to Binary Conversion ................................................................................................................. 51.4 Octal Number System .............................................................................................................................. 7 1.4.1 Octal to Decimal Conversion ................................................................................................... 7 1.4.2 Decimal to Octal Conversion ................................................................................................... 7 1.4.3 Octal to Binary Conversion ..................................................................................................... 8 1.4.4 Binary to Octal Conversion ..................................................................................................... 91.5 Hexadecimal Number System .................................................................................................................. 9 1.5.1 Hex to Decimal Conversion ................................................................................................... 10 1.5.2 Decimal to Hex Conversion ....................................................................................................11 1.5.3 Hex to Binary Conversion ..................................................................................................... 12 1.5.4 Binary to Hex Conversion ..................................................................................................... 12 1.5.5 Hex to Octal Conversion ........................................................................................................ 12 1.5.6 Octal to Hex Conversion ........................................................................................................ 121.6 Codes...................................................................................................................................................... 13 1.6.1 BCD Code .............................................................................................................................. 13 1.6.2 ASCII Code ............................................................................................................................ 13 1.6.3 Code Gray .............................................................................................................................. 131.6.4 Excess 3 131.7 Binary Arithmetic ................................................................................................................................... 14 1.7.1 Addition ................................................................................................................................. 14 1.7.1.1 Addition of Signed Numbers ................................................................................... 15 1.7.1.2 Subtraction .............................................................................................................. 15 1.7.2 Multiplication ......................................................................................................................... 16 1.7.3 Division .................................................................................................................................. 16Summary ..................................................................................................................................................... 33References ................................................................................................................................................... 18Recommended Reading ............................................................................................................................. 18Self Assessment ........................................................................................................................................... 19

Chapter II ................................................................................................................................................... 21Logic Gates ................................................................................................................................................. 21Aim .............................................................................................................................................................. 21Objectives .................................................................................................................................................... 21Learning outcome ........................................................................................................................................ 212.1 Introduction ............................................................................................................................................ 222.2 Logic Gates ............................................................................................................................................ 22 2.2.1 NOT Gate ............................................................................................................................... 22 2.2.2 OR Gate ................................................................................................................................. 22 2.2.3 AND Gate .............................................................................................................................. 22 2.2.4 NAND Gate ........................................................................................................................... 23 2.2.5 NOR Gate .............................................................................................................................. 23 2.2.6 XOR Gate .............................................................................................................................. 23 2.2.7 XNOR .................................................................................................................................... 232.3 Truth Tables ............................................................................................................................................ 25 2.3.1 Description of the six logic gates ........................................................................................... 25

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2.4 Logic circuits/networks .......................................................................................................................... 28Summary ..................................................................................................................................................... 33References ................................................................................................................................................... 33Recommended Reading ............................................................................................................................. 33Self Assessment ........................................................................................................................................... 34

Chapter III .................................................................................................................................................. 36Computer Components and Information Processing Cycle .................................................................. 36Aim .............................................................................................................................................................. 36Objectives .................................................................................................................................................... 36Learning outcome ........................................................................................................................................ 363.1 Introduction ............................................................................................................................................ 373.2 Components ........................................................................................................................................... 373.3 Input Devices ......................................................................................................................................... 37 3.3.1 Keyboard ................................................................................................................................ 37 3.3.2 Pointing Devices .................................................................................................................... 38 3.3.3 Pen Input Devices .................................................................................................................. 38 3.3.4 Video Input Devices ............................................................................................................... 38 3.3.5 Audio Input Devices .............................................................................................................. 39 3.3.6 Graphic Capture Devices ....................................................................................................... 39 3.3.7 Code Numbers ....................................................................................................................... 39 3.3.8 Optical Input Devices ............................................................................................................ 403.4 Central Processing Unit ......................................................................................................................... 40 3.4.1 Arithmetic Logic Unit (ALU) ................................................................................................ 40 3.4.2 Control Unit (CU) .................................................................................................................. 41 3.4.3 Primary Memory .................................................................................................................... 413.5 Output Devices ....................................................................................................................................... 42 3.5.1 Visual Output Devices (Soft copy) ........................................................................................ 43 3.5.2 Audio Output Devices (Soft copy) ......................................................................................... 43 3.5.3 Hardcopy Devices (print and film) ........................................................................................ 44 3.5.4 Computer Output Microfilms (COM) .................................................................................... 443.6 Data Storage ........................................................................................................................................... 44 3.6.1 Auxiliary Storage/Secondary Storage .................................................................................... 44 3.6.2 Magnetic Disk ....................................................................................................................... 45 3.6.3 Magnetic Tapes ...................................................................................................................... 46 3.6.4 Optical Disks .......................................................................................................................... 46 3.6.5 Flash Memory ........................................................................................................................ 48 3.6.6 USB Drives ............................................................................................................................ 48 3.6.7 Removable Hard Drives ......................................................................................................... 48 3.6.8 Smart Cards ............................................................................................................................ 49 3.6.9 Optical Cards ......................................................................................................................... 49Summary ..................................................................................................................................................... 50References ................................................................................................................................................... 50Recommended Reading ............................................................................................................................. 50Self Assessment ........................................................................................................................................... 51

Chapter IV .................................................................................................................................................. 53Hardware and Software ............................................................................................................................ 53Aim .............................................................................................................................................................. 53Objectives .................................................................................................................................................... 53Learning outcome ........................................................................................................................................ 534.1 Introduction ........................................................................................................................................... 544.2 Hardware ............................................................................................................................................. 54 4.2.1 Motherboard ........................................................................................................................... 544.3 Software ............................................................................................................................................. 54

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4.4 Programming Languages ....................................................................................................................... 55 4.4.1 Machine Language ................................................................................................................. 55 4.4.2 Assembly Language ............................................................................................................... 55 4.4.3 High Level Language ............................................................................................................. 55 4.4.4 Fourth Generation Language ................................................................................................. 55 4.4.5 Natural Language ................................................................................................................... 564.5 Systems Software ................................................................................................................................... 56 4.5.1 BIOS ...................................................................................................................................... 56 4.5.2 Operating System (OS) .......................................................................................................... 56 4.5.3 Utility Software ...................................................................................................................... 584.6 Application Software ............................................................................................................................. 58Summary ..................................................................................................................................................... 60References ................................................................................................................................................... 60Recommended Reading ............................................................................................................................. 60Self Assessment ........................................................................................................................................... 61

Chapter V .................................................................................................................................................... 63Communication and Networks ................................................................................................................. 63Aim .............................................................................................................................................................. 63Objectives .................................................................................................................................................... 63Learning outcome ........................................................................................................................................ 635.1 Introduction ............................................................................................................................................ 645.2 Computer Networks ............................................................................................................................... 645.3 Goals of Networks ................................................................................................................................. 645.4 Communication Channels ...................................................................................................................... 645.4.1 Wired Channels (Twisted-pair Wire, Coaxial Cable and Fibre-optic Cable) ...................................... 655.4.2 Wireless Channels (Radio Link, Microwave Link, Satellite Communication) .................................. 665.5 Transmission Technology ...................................................................................................................... 67 5.5.1 Broadcast Networks .............................................................................................................. 67 5.5.2 Point-to-Point or Switched Networks ................................................................................... 68 5.5.3 Bandwidth .............................................................................................................................. 685.6 Network Configuration .......................................................................................................................... 69 5.6.1 Client-Server Network ........................................................................................................... 69 5.6.2 Peer-to-peer Network ............................................................................................................. 695.7 Network Models ..................................................................................................................................... 69 5.7.1 OSI Reference Model ............................................................................................................ 69 5.7.2 TCP/IP Protocol ..................................................................................................................... 725.8 Network Topologies ............................................................................................................................... 725.9 Types of Networks ................................................................................................................................. 76Summary ..................................................................................................................................................... 78References ................................................................................................................................................... 78Recommended Reading ............................................................................................................................. 78Self Assessment ........................................................................................................................................... 79

Chapter VI .................................................................................................................................................. 81Operating Systems ..................................................................................................................................... 81Aim .............................................................................................................................................................. 81Objectives .................................................................................................................................................... 81Learning outcome ........................................................................................................................................ 816.1 Introduction ............................................................................................................................................ 826.2 Operating System ................................................................................................................................... 82 6.2.1 Functions of Operating System .............................................................................................. 82 6.2.2 Operating System as User Interface ....................................................................................... 826.3 History of Operating System ................................................................................................................. 846.4 Disk Operating System ......................................................................................................................... 84

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6.4.1 History of DOS ..................................................................................................................... 84 6.4.2 Components of MS-DOS ....................................................................................................... 84 6.4.3 Internal Command ................................................................................................................. 85 6.4.4 External Commands ............................................................................................................... 886.5 UNIX ...................................................................................................................................................... 90 6.5.1 MEM ...................................................................................................................................... 90 6.5.2 FILTER .................................................................................................................................. 91 6.5.3 ATTRIB .................................................................................................................................. 92 6.5.4 DELTREE .............................................................................................................................. 92 6.5.5 EDIT ...................................................................................................................................... 926.6 Batch Files ............................................................................................................................................. 926.7 Batch System ......................................................................................................................................... 936.8 Time Sharing Systems............................................................................................................................ 946.9 Multiprogramming ................................................................................................................................. 956.10 Spooling ............................................................................................................................................. 966.11 Essential Properties of the Operating System Batch ............................................................................ 96 6.11.1 Time Sharing ........................................................................................................................ 96 6.11.2 Interactive ............................................................................................................................ 96 6.11.3 Real time system .................................................................................................................. 97 6.11.4 Distributed ............................................................................................................................ 97Summary ..................................................................................................................................................... 98References ................................................................................................................................................... 98Recommended Reading ............................................................................................................................. 99Self Assessment ......................................................................................................................................... 100

Chapter VII .............................................................................................................................................. 102Data processing ........................................................................................................................................ 102Aim ............................................................................................................................................................ 102Objectives .................................................................................................................................................. 102Learning outcome ...................................................................................................................................... 1027.1 Introduction .......................................................................................................................................... 103 7.1.1 Data ...................................................................................................................................... 104 7.1.2 Information .......................................................................................................................... 104 7.1.3 Types of Data ....................................................................................................................... 1047.2 Input, Processing and output ................................................................................................................ 104 7.2.1 Input ..................................................................................................................................... 104 7.2.2 Processing ............................................................................................................................ 105 7.2.3 Output .................................................................................................................................. 1057.3 Architecture of Computer System ........................................................................................................ 105 7.3.1 The Control Unit (CU) ......................................................................................................... 105 7.3.2 The Immediate Access Store (IAS)...................................................................................... 106 7.3.3 ALU stands for Arithmetic and Logic Unit. ........................................................................ 1067.4 Concepts of Files .................................................................................................................................. 106 7.4.1 File contents ......................................................................................................................... 106 7.4.2 Operations on the file ........................................................................................................... 107 7.4.3 File Organisation .................................................................................................................. 107 7.4.4 Relative File ......................................................................................................................... 108 7.4.5 Indexed Files ........................................................................................................................ 1097.5 Protecting Files .....................................................................................................................................1107.6 Storing files ...........................................................................................................................................110 7.6.1 Backing up files ....................................................................................................................1107.7 File Terminology ...................................................................................................................................111 7.7.1 Records .................................................................................................................................111 7.7.2 Fields .....................................................................................................................................1127.8 Data Capturing ......................................................................................................................................112


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7.8.1 Direct Data Capturing ...........................................................................................................112 7.8.2 Data Capture Forms ..............................................................................................................1137.9 Verification ............................................................................................................................................114 7.9.1 Editing and Checking ............................................................................................................115Summary ....................................................................................................................................................117References ..................................................................................................................................................117Recommended Reading ............................................................................................................................118Self Assessment ..........................................................................................................................................119

Chapter VIII ............................................................................................................................................. 121Internet and Network Security .............................................................................................................. 121Aim ............................................................................................................................................................ 121Objectives .................................................................................................................................................. 121Learning outcome ...................................................................................................................................... 1218.1 Internet ................................................................................................................................................. 1228.2 Internet Architecture ............................................................................................................................ 122 8.2.1 Protocol ................................................................................................................................ 122 8.2.2 IP Address ........................................................................................................................... 122 8.2.3 Domain Name Service ......................................................................................................... 122 8.2.4 Packet Switching .................................................................................................................. 122 8.2.5 Internet Routers .................................................................................................................... 123 8.2.6 Backbones ............................................................................................................................ 1238.3 Network Security ................................................................................................................................. 123 8.3.1 Understanding Potential Threats .......................................................................................... 123 8.3.2 Steps towards Security ......................................................................................................... 1248.4 Uses of Internet .................................................................................................................................... 125Summary ................................................................................................................................................... 126References ................................................................................................................................................. 126Recommended Reading .......................................................................................................................... 126Self Assessment ......................................................................................................................................... 127

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List of Figures

Fig. 1.1 Positional value (weight) of each bit ................................................................................................ 2Fig. 1.2 1’s complement ................................................................................................................................. 3Fig. 1.3 (a) Decimal to binary conversion ..................................................................................................... 5Fig. 1.3 (b) Decimal to binary conversion ..................................................................................................... 5Fig. 1.4 (a) Decimal to binary conversion ..................................................................................................... 6Fig. 1.4 (b) Decimal to binary conversion ..................................................................................................... 6Fig. 1.5 Octal number system ........................................................................................................................ 7Fig. 1.6 (b) Decimal to octal conversion ........................................................................................................ 8Fig. 1.7 Hexadecimal number showing positional values (weight) of digits ............................................... 10Fig. 1.8 (a) Decimal to hex conversion .........................................................................................................11Fig. 1.8 (b) Decimal to hex conversion .........................................................................................................11Fig. 2.1 Logic gates (a) Basic logic gates; (b) Compound logic gates (c) Truth tables for compound gates 24Fig. 2.2 Not gate ........................................................................................................................................... 25Fig. 2.3 AND gate ........................................................................................................................................ 25Fig. 2.4 OR gate ........................................................................................................................................... 26Fig. 2.5 NAND gate ..................................................................................................................................... 26Fig. 2.6 NOR gate ........................................................................................................................................ 27Fig. 2.7 XOR gate ........................................................................................................................................ 27Fig. 2.8 Logic circuit .................................................................................................................................... 30Fig. 2.9 Logic circuit .................................................................................................................................... 32Fig. 2.10 Logic circuit .................................................................................................................................. 32Fig. 3.1 Schematic representation of a computer system ............................................................................ 37Fig. 3.2 Disk sectors..................................................................................................................................... 45Fig. 3.3 Track sectors ................................................................................................................................... 45Fig. 3.4 Logical layout of magnetic disk ..................................................................................................... 46Fig. 5.1 OSI reference model ....................................................................................................................... 70Fig. 5.2 Bus topology ................................................................................................................................... 73Fig. 5.3 Star topology................................................................................................................................... 74Fig. 5.4 Ring topology ................................................................................................................................. 74Fig. 5.5 Tree topology .................................................................................................................................. 75Fig. 5.6 Mesh topology ................................................................................................................................ 76Fig. 6.1 Conceptual view of a computer system .......................................................................................... 83Fig. 6.2 Memory layout for a simple batch system ...................................................................................... 93Fig. 6.3 Memory layout for a multiprogramming system ............................................................................ 95Fig. 6.4 Spooling .......................................................................................................................................... 96Fig. 7.1 Block diagram of CPU ................................................................................................................. 105Fig. 7.2 Relative File - Organisation .......................................................................................................... 108Fig. 7.3 Files and folders arranged in a hierarchy ...................................................................................... 109Fig. 7.4 Sample data capture form ..............................................................................................................114Fig. 7.5 Form filled by the customer ...........................................................................................................114


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List of Tables

Table 1.1 Counting binary numbers ............................................................................................................... 3Table 1.2 Binary equivalent of octal digit ...................................................................................................... 9Table 1.3 Binary and decimal equivalent of each hex digit ......................................................................... 10Table 1.4 Gray code ..................................................................................................................................... 13Table 1.5 One-bit binary addition ................................................................................................................ 15Table 2.1 Truth table .................................................................................................................................... 31Table 5.1 Types of networks ........................................................................................................................ 77Table 6.1 History of OS ............................................................................................................................... 84Table 6.2 Some Special $ Parameters Are Given Below ............................................................................. 88Table 7.1 Types of Data ............................................................................................................................. 104Table 7.2 File terminology ..........................................................................................................................111Table 7.3 Records ........................................................................................................................................111Table 7.4 Fields ...........................................................................................................................................112Table 7.5 Types of validation ......................................................................................................................116Table 8.1 Types of threats and consequences............................................................................................. 123

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Abbreviations

ASCII - American Standard Code for Information InterchangeBCD - Binary Coded DecimalBJT - Bipolar Junction Transistor CML - Current Mode Logic CMOS - Complementary Metal Oxide Semiconductor D Flip Flop - Data Flip FlopDEMUX - Demultiplexer DL - Diode Logic DTL - Diode Transistor Logic ECL - Emitter Coupled Logic F - False FET - Field Effect TransistorFF - Flip FlopsH (1) - HighHex - Hexadecimal IC - Integrated CircuitIGFET - Insulated-gate FET IIL - Integrated Injection Logic JFET - Junction FET K-map - Karnaugh MapL (0) - Low LSB - LeastSignificantBitMOSFET - Metal-oxide- semiconductor FET MSB - MostSignificantBitMUX - Multiplexer NMOS - N-channel MOSFETsPMOS - P-channel MOSFETsP-N Junction - Positive type (P) and Negative type (N)POS - Product of Sums RTL - Resistor Transistor Logic SOP - Sum-of-Products Equations S-R Flip-Flop - SET-RESET Flip FlopT Flip Flop - Toggle Flip FlopT - True TTL - Transistor Transistor Logic XS-3 - Excess-3 Binary-coded Decimal

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Chapter I

Number System and Codes

Aim

The aim of this chapter is to:

explain different types of number systems•

elucidate binary arithmetic•

explicate different types of codes•

Objectives

The objectives of this chapter are to:

explain conversion of digits from a number system to another•

elucidate binary system and binary arithmetic•

explicate inter-conversion of digits from one number system to another•

Learning outcome

At the end of this chapter, you will be able to:

understand number system into decimal, binary, octal and hex number systems•

describe methods of binary arithmetic•

classify BCD, ASCII and code gray•


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1.1 IntroductionNumber system is simply the ways to count things. Aim of any number system is to deal with certain quantities which can be measured, monitored, recorded, manipulated arithmetically, observed and utilised. Each quantity has to be representedbyitsvalueasefficientlyandaccuratelyasisnecessaryforanyapplication.Thenumericalvalueofaquantity can be basically expressed in either analog (continuous) or digital (step by step) method of representation. Inanalogmethod,aquantityisexpressedbyanotherquantitywhichisproportionaltothefirst.Forexample,thevoltageoutputofanamplifierismeasuredbyavoltmeter.

Theangularpositionoftheneedleofthevoltmeterisproportionaltothevoltageoutputoftheamplifier.Yetanotherexample is of a thermometer. The height to which the mercury rises is proportional to the temperature. In both these examples, the value of voltage and temperature can be anywhere between zero and the maximum limit. In digital method, the value of a quantity is expressed by some symbols which are called digits, and not by a quantity which isproportionaltothefirst.Inadigitalwatch,thetime,whichchangescontinuously,isexpressedbydigitswhichdonot change continuously. It is clear from the examples that the accuracy of the value of an analog quantity generally depends upon the judgement of the observer.

Digital technology is different from analog technology. Many number systems are being used in digital technology. Most common amongst them are decimal, binary, octal, and hexadecimal systems.

We are most familiar with the decimal number system, because we use it every day.It is the base-10 or radix-10 system. Note that there is no symbol for “10” or for the base of any system. We count 123456789,andtheninserta0inthefirstcolumnandaddanewleftcolumn,startingat1again.Thenwecount1-9inthefirstcolumnagain.(Peopleusethebase-10systembecausewehave10fingers!).Eachcolumninour system stands for a power of 10 starting at 100.

All computers use the binary system. Following section provides an overview of the binary system.

1.2 Binary SystemIn the binary number system (base of 2), there are only two digits: 0 and 1 and the place values are 2• 0, 21, 22, 23 etc. Binary digits are abbreviated as bits. For example, 1101 is a binary number of 4 bits (ie., it is a binary number containing four binary digits.)A binary number may have any number of bits. Consider the number 11001.01 1. Note the binary point •(counterpart of decimal point in decimal number system) in this number. Each digit is known as a bit and can take only two values 0 and 1. The left most bit is the highest-order bit and •representsthemostsignificantbit(MSB)whilethelowest-orderbitistheleastsignificantbit(LSB).Someusefuldefinitionsare:

Word � is a binary number consisting of an arbitrary number of bits.Nibble � is a 4-bit word (one hexadecimal digit) 16 values.Byte � is an 8-bit word 256 values.

24 23 22 21 20 2-1 2-2 2-3

1 1 0 0 1 0 1 1

Positional values or weight

MSB Binary Point LSB

Fig. 1.1 Positional value (weight) of each bit(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

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Any number can be expressed in binary form in the usual way. Table 2.1 shows expression of binary numbers.

23 22 21 20 Binary Number Decimal Number

0000000011111111

0000111100001111

0011001100110011

0101010101010101

0000000100100011010001010110011110001001101010111100110111101111

0123456789101112131415

Table 1.1 Counting binary numbers(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

1’s complementThe 1’s complement of a binary number is obtained just by changing each 0 to 1 and each 1 to 0.

Binary number 1 0 1 1 1 0 1 0

1-complement 1 0 1 1 1 0 1 0

Fig. 1.2 1’s complement(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

2’s complementThe 2’s complement of a binary number is obtained adding 1 to the 1’s complement of this number:

2’s complement = 1’s complement+1Binary number 1 0 1 1 1 0 1 01’s complement 0 1 0 0 0 1 0 1 + 12’s complement 0 1 0 0 0 1 1 0

There is a simple method to obtain the 2’s complement:BeginningwiththeLSB,justwritedownbitsastheyaremovingtolefttillthefirst1,includingit.•Substitute the rest of bits by their 1’s complement.•


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Signed numbersIn a signed number, the left most bit is the so called sign bit: 0=positive number 1=negative number.

Sign-value notation In this notation, the left-most bit is the sign bit and the others are used to represent the absolute value notation.

1’s complement In this notation, the positive numbers have the same representation as the sign-value notation, and the negative numbers are obtained by taking the 1’s complement of the positive correspondents.

2’s complement The positive numbers have the same representation as the sign-value notation, and the negative numbers are obtained by taking the 1’s complement of the positive correspondents.Positive All 00011001 (+25)Negative Sign-value 100110011’s complement 111001102’s complement 11100111

1.2.1 Binary to Decimal ConversionBinary number can be converted into its decimal equivalent, by simply adding the weights of various positions in the binary number which have bit 1.

Example1 Find the decimal equivalent of the binary number (11111)2 The equivalent decimal number is =1X24+1X23+1X22+1X21+1X20

=16+8+4+2+1 = (31)10

To differentiate between numbers represented in different number systems, either the corresponding number •systemmaybespecifiedalongwiththenumberorasmallsubscriptattheendofthenumbermaybeaddedsignifying the number system. Example (1000)2 represents a binary number and is not one thousand.

Example 2 Consider the conversion of (100011.101)2 1 0 0 0 1 1.1 0 1 = 25+0+0+0+21+20+2-1+0+2-3 =32+2+1+0.5+0.125 =(35.625)10 Consider the following examples. 1111.00 = 15 11110.0 = 30 111100.0 = 60 From these examples, it is clear that if the binary point is shifted towards right side, then the value of the number is doubled. Now consider the following examples. 111.100 = 7.5 11.1 100 = 3.75 1.1 1100 = 1.875 From these examples it is clear that if the binary point is shifted towards the left side, then the value of the number is halved.

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1.3 Decimal to Binary ConversionA decimal number is converted into its binary equivalent by its repeated divisions by 2. The division is continued tillwegetaquotientof0.Thenalltheremaindersarearrangedsequentiallywithfirstremaindertakingthepositionof LSB and the last one taking the position of MSB. Consider the conversion of 27 into its binary equivalent as follows.

2

2

2

2

2

27

13 - 1

- 1

- 0

6

3

1

- 0

0 - 1

1 1 0 1 1

Thus 2710= 110112

Fig. 1.3 (a) Decimal to binary conversion(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

Ifthenumberalsohassomefiguresontherightofthedecimalpoint,thenthispartofthenumberistobetreatedseparately.Multiplythispartrepeatedlybytwo.Afterfirstmultiplicationby2,either1or0willappearontheleftof the decimal point. Keep this 1 or 0 separately and do not multiply it by 2 subsequently. This should be followed for every multiplication. Continue multiplication by 2 till you get all 0s after the decimal point or up to the level of the accuracy desired. This will be clear from the following example. Consider the conversion of 27.62510 into its binary equivalent. We have already converted 27 into its binary equivalent which is (11011)2. Now for the conversion of 0.625, multiply it by 2 repeatedly as follows: Thus, 27.62510 = 11011.101

.625x 21.250

.250x 20.500

.500x 2

1.000

1 0 1.000

Fig. 1.3 (b) Decimal to binary conversion(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)


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Let us try another example, conversion of (58.0725)10 into binary. Split this number in two parts, i.e., 58 and .0725 and convert them into binary separately as described above.

1 1 1 0 1 0

2

2

2

2

2

2

58

0 - 1

— 1

— 1

— 0

— 1

— 029

14

7

3

1

Fig. 1.4 (a) Decimal to binary conversion(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

Now let's look at the conversion of 0.725 Thus, (58.0725)10 = 111010.00010

.0725x 2

0.1450.1450x 2

0.2900.2900x 2

0.5800

1 0

.5800x 2

1.1600

1

.1600x 2

0.3200

01

Fig.1.4 (b) Decimal to binary conversion(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

Representing numbers in binary is very tedious, since binary numbers often consist of a large chain of 0's and 1's. Convenient shorthand forms for representing the binary numbers are developed such as octal system and hexadecimal

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system. With these number systems long strings of 0's and 1's can be reduced to a manageable form. The section below gives an overview of these systems.

1.4 Octal Number SystemThe octal number system has base-8 that is, there arc 8 digits in this system. These digits are 0, 1, 2, 3, 4, 5, 6, and 7. The weight of each octal digit is some power of 8 depending upon the position of the digit. Octal numbers showing positional values (weights) of each digit are as follows:

84 83 82 81 80 8-1 8-2 Weights

1 0 6 2 7 4 5 Octal Number

MSD Octal LSD Point

Fig. 1.5 Octal number system(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

Octal number does not include the decimal digits 8 and 9. If any number includes decimal digits 8 and 9, then the number can not be an octal number.

1.4.1 Octal to Decimal ConversionAs has been done in case of binary numbers, an octal number can be converted into its decimal equivalent by multiplying the octal digit by its positional value. For example,let us convert 36.48 into decimal number.36.48 = 3 x 81 + 6 x 80 + 4 x 8-1

= 24 + 6 + 0.5= (30.5)10

1.4.2 Decimal to Octal ConversionA decimal number can be converted by repeated division by 8 into equivalent octal number. This method is similar to that adopted in decimal to binary conversion. If the decimal number has some digits on the right of the decimal point, then this part of the number is converted into its octal equivalent by repeatedly multiplying it by 8. The process is same as has been followed in binary number system. Consider the conversion of 126.3810 into its decimal equivalent. Split it into two parts, that is 126 and .38


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126

15 — 6

1 — 7

0 — 1

8

8

8

8

1 7 6

Fig. 1.6 (a) Decimal to octal conversion(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

The conversion of .38 is as follows Thus, (126.38)10 = 176.3024

.38x 83.04

3

.04x 80.32

0

.56x 84.48

4

.48

.32x 82.56

2

Fig. 1.6 (b) Decimal to octal conversion(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

2.4.3 Octal to Binary ConversionIn the octal number system the highest octal digit, i.e., 7 can be expressed as a 3-bit binary number. Therefore, all the octal digits have to be represented by n 3-bit binary number. The binary equivalent of each octal digit is shown in Table 1.2. The main advantage of the octal number system is the easiness with which any octal number can be

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converted into its binary equivalent.

Octal digit 3-bit binary equivalent

0

1

2

3

4

5

6

7

000

001

010

011

100

101

110

111

Table 1.2 Binary equivalent of octal digit(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

Using this conversion of octal digit into 3-bit binary number, any octal number can be converted into its binary equivalent by simply replacing each octal digit by a 3-bit binary number. For example, conversion of 567, into its binary equivalent is:567 = 101110111

1.4.4 Binary to Octal ConversionAbinarynumbercanbeconvertedintoitsoctalequivalentbyfirstmakinggroupsof3-bitsstartingfromtheLSBside. If the MSB side does not have 3 bits, then add 0s to make the last group of 3 bits. Then by replacing each group of 3 bits by its octal equivalent, a binary number can be converted into its binary equivalent. For example, consider the conversion of 1100011001, into its octal equivalent as follows:= 001 100 01 1 001 [As the MSB side does not have 3 bits, we have added two 0's to make the last group of 3 bits]= l 4 3 1

Thus, (1100011001)2 = (1431)8

1.5 Hexadecimal Number SystemThe hexadecimal number system has base 16 that is it has 16 digits (Hexadecimal means'16'). These digits are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F. The digits A, B, C, D, E and F have equivalent decimal values 10, 11, 12, 13, 14, and 15 respectively. Each Hex (Hexadecimal is popularly known as hex) digit in a hex number has a positional value that is some power of 16 depending upon its position in the number.


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164 163 162 161 160 16-1 16-2 Weights 1 2 4 A B B 9 Hex number

MSD Hex LSD Point

Fig. 1.7 Hexadecimal number showing positional values (weight) of digits(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

Relationship of hex digits with decimal and binary numbers is given in Table 1.3. Note that to represent the largest hex digit we require four binary bits. Therefore, the binary equivalent of all the hex digits has to be written in four bit numbers.

Hex digit Decimal equivalent 4-bit Binary equivalent

0123456789ABCDEF

0123456789101112131415

0000000100100011010001010110011110001001101010111100110111101111

Table 1.3 Binary and decimal equivalent of each hex digit(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

1.5.1 Hex to Decimal ConversionHex to decimal conversion is done in the same way as in the cases of binary and octal to decimal conversions. A hex number is converted into its equivalent decimal number by summing the products of the weights of each digit and their values. This is clear from the example of conversion of 514.AF16 into its decimal equivalent.

514. AF16 = 5 X 162 + 1 X 161 + 4 X 160 + 10 X 16-1 + 15 X 16-2

= 1280+16+4+0.625+0.0586 = (1300.6836)10

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1.5.2 Decimal to Hex ConversionA decimal number is converted into hex number in the same way as a decimal number is converted into its equivalent binary and octal numbers. The part of the number on theleft of the decimal point is to be divided repeatedly by 16 and the part an the right ofthe decimal point is to be repeatedly multiplied by 16. This will be clear from theexamples of conversion of (579.26)10 into hex equivalent. Split the number into two parts, 579 and .26.

Thus, (579)10 = (2443)16

579

36 — 3

2 — 4

0 — 2

16

16

16

2 4 3

Fig. 1.8 (a) Decimal to hex conversion(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)

Now .26 is converted into hex number as follows:

.96

.26x 164.16

4

.16x 162.56

2

.56x 168.96

8Thus 579.2610=243.42816

Fig. 1.8 (b) Decimal to hex conversion(Source: http://www.egyankosh.ac.in/bitstream/123456789/10991/1/Unit-10.pdf)


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1.5.3 Hex to Binary ConversionAs in octal number system, a hex number is converted into its binary equivalent by replacing each hex digit by its equivalent 4-bit binary number. This is clear from the following example:

(BA6)16 = B A 6 = 1011 1010 010 = (101110100110)2

1.5.4 Binary to Hex ConversionBy a process that is reverse of the process described in the above section, a binary number can be converted in to its hex equivalent. Starting from the LSB side, group the binary number bits into groups of lour bits. If towards the MSB side, the numbers of bits is less than four, then add zeros on the left of the MSB so that the group of four is complete. Replace each group by its equivalent hex digit. This is clear from the following example:

(1001101110)2 = 0010 0110 1110 = 2 6 E = (26E)16

1.5.5 Hex to Octal ConversionEachdigitof thehexnumber isfirstconverted into itsequivalent fourbitbinarynumber.Then thebitsof theequivalent binary number are grouped into groups of three bits. Then each group is replaced by its equivalent octal digit to get the octal number.For example:(5AF)16 = 0101 1010 1111 = 010110101111 =010 110 101 111 = 2 6 5 7 =(2567)8

1.5.6 Octal to Hex ConversionFor octal to hex conversion, just reverse the process described in the section above.This is clear from the following example:(5457)8 = 101 100 101 111 = 1011 0010 1111 = B 2 F = (B2F)16

This method can also be applied to hex to decimal and decimal to hex conversions. For example, consider the conversion of 3C16, into its decimal equivalent:

3C16 = 0011 1100 = 1111002Check the conversion.3C16 = 3 X161 + C X160

= 3 x 161+ 12 x 160

= 48 + 12 = (60)101111002 = 25+24+23+22

= 32+16+8+4= (60)10Thus, 3C16 = (111100)2 = 6010

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1.6 CodesWe had an overview of binary, octal and hexadecimal number system. For any number system with n base B and digits N0 (LSB), N1 N2...... N10 (M SB), the decimal equivalent N10 is given by

Whennumbers,lettersorwordsarerepresentedbyaspecificgroupofsymbols,itissaidthatthenumber,letterorword is being encoded. The group of symbols is called as the code.Few codes will be discussed in the following sections.

1.6.1 BCD CodeIn BCD (BCD stands Binary coded decimal) code, each digit of a decimal number is converted in to its binary equivalent. The largest decimal digit is 9; therefore the largest binary equivalent is 1001. This is illustrated as follows951 10 = 1001 0101 0001 = (100101010001)BCD

1.6.2 ASCII CodeThe word ASCII is run acronym of American Standard Code for Information Interchange. This is the alphanumeric code most widely used in computers. The alphanumeric code is one that represents alphabets, numerical numbers, punctuation marks and other special characters recognised by a computer. The ASCII code is a 7-bit code representing 26 English alphabets, 0 through 9 digits, punctuation marks, etc. A 7-bit code has 27 = 128 possible code groups whicharcquitesufficient.

1.6.3 Code GrayGray Code is a form of binary that uses a different method of incrementing from one number to the next. With Gray Code, only one bit changes state from one position to another. This feature allows a system designer to perform some error checking (i.e., if more than one bit changes, the data must be incorrect).

Decimal Binary Gray Decimal Binary Gray

0 0000 0000 8 1000 1100

1 0001 0001 9 1001 1101

2 0010 0011 10 1010 1111

3 0011 0010 11 1011 1110

4 0100 0110 12 1100 1010

5 0101 0111 13 1101 1011

6 0110 0101 14 1110 1001

7 0111 0100 15 1111 1000

Table 1.4 Gray code(Source: http://dpnc.unige.ch/tp/elect/doc/07-Digital.pdf)

1.6.4 Excess 3

Excess-3 binary-coded decimal (XS-3), also called biased representation or Excess-N, is a numeral system used •onsomeoldercomputersthatusesapre-specifiednumberNasabiasingvalue.Itisawaytorepresentvalueswith a balanced number of positive and negative numbers. In XS-3, numbers are represented as decimal digits, and each digit is represented by four bits as the BCD value plus 3 (the "excess" amount)


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Thesmallestbinarynumberrepresentsthesmallestvalue.(i.e.0−ExcessValue)•The greatest binary number represents the largest value. (i.e. 2• N+1−ExcessValue−1)The primary advantage of XS-3 coding over BCD coding is that a decimal number can be 9’s complemented •(for subtraction) as easily as a binary number can be 1's complemented; just invert all bits. In addition, when the sum of two XS-3 digits is greater than 9, the carry bit of a four bit adder will be set high. This works because, when adding two numbers that are greater or equal to zero, an "excess" value of six results in the sum. Since a fourbitintegercanonlyholdvalues0to15,anexcessofsixmeansthatanysumoverninewilloverflow.

1.7 Binary ArithmeticMajority of arithmetic performed by computers is binary arithmetic, that is, arithmetic on base two numbers. Decimalandfloating-pointnumbers,alsousedincomputerarithmetic,dependonbinaryrepresentations,andanunderstanding of binary arithmetic is necessary in order to understand either one.

Computersperformarithmeticonfixed-sizenumbers.Thearithmeticoffixedsizenumbersiscalledfinite-precisionarithmetic.Therulesforfinite-precisionarithmeticaredifferentfromtherulesofordinaryarithmetic.Thesizesof numbers which can be arithmetic operands are determined when the architecture of the computer is designed. Common sizes for integer arithmetic are eight, 16, 32, and recently 64 bits. It is possible for the programmer to perform arithmetic on larger numbers or on sizes which are not directly implemented in the architecture. However, this is usually so painful that the programmer picks the most appropriate size implemented by the architecture. This puts a burden on the computer architect to select appropriate sizes for integers, and on the programmer to be aware ofthelimitationsofthesizehehaschosenandonfinite-precisionarithmeticingeneral.

We are considering binary arithmetic in the context of building digital logic circuits to perform arithmetic. Not only dowehavetodealwiththefactoffiniteprecisionarithmetic,wemustconsiderthecomplexityofthedigitallogic.When there is more than one way of performing an operation we choose the method which results in the simplest circuit.

1.7.1 AdditionAddition of binary numbers can be carried out in a similar way by the column method But before this, view four simple cases. In the decimal number system, 3 + 6 = 9 symbolizes the combination of 3 with 6 to get a total of 9.

View the four simple cases.Case 1: • When nothing is combined with nothing, we get nothing. The binary representation of this is 0 + 0 = 0.Case 2: • When nothing is combined with1, we get1. Using binary numbers to denote this gives 0 + 1 = 1.Case 3: • Combining.1 with nothing gives 1. The binary equivalent of this is 1 + 0 = 1.Case 4:• When we combine 1 with 1, the result is 2. Using binary numbers, we symbolize 1 + 1 = 10.

The last result is sometimes confusing because of our long time association with decimal numbers. But it is correct and makes sense because we are using binary numbers. Binary number 10 stands for'1','0' and not for 10 (ten). To summarize our results for binary addition,

0+0 = 0 �0+1 = 1 �1+0 = 1 �1+1=10 �

One can also express the rules of binary addition with a truth table. This is important because there are techniques •for designing electronic circuits that compute functions expressed by truth tables. The fact that we can express the rules of binary addition as a truth table implies that we can design a circuit which will perform addition on binary numbers, and that turns out to be the case.

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We only need to write the rules for one column of bits; we start at the right and apply the rules to each column •insuccessionuntilthefinalsumisformed.CallthebitsoftheaddendandaugendAandB,andthecarryinfrom the previous column Ci. Call the sum S and the carry out Co. The truth table for one-bit binary addition looks like this:•

A B Ci S Co0 0 0 0 00 0 1 1 00 1 0 1 00 1 1 0 11 0 0 1 01 0 1 0 11 1 0 0 11 1 1 1 1

Table 1.5 One-bit binary addition

This says if all three input bits are zero, both S and Co will be zero. If any one of the bits is one and the other two are zero, S will be one and Co will be zero. If two bits are 1's, S will be zero and Ci will be one. Only if all three bits are 1's, both S and Co will be 1's.

1.7.1.1 Addition of Signed NumbersBinary addition of 2’s complement signed numbers can be performed using the same rules given above for unsigned addition. If there is a carry out of the sign bit, it is ignored.Itispossiblefortheresultofanadditiontobetoolargetofitintheavailablespace.Theanswerwillbetruncated,andwillbeincorrect.Thisistheoverflowconditiondiscussedabove.Therearetworulesfordeterminingwhetheroverflowhasoccurred:

Iftwonumbersofoppositesignsareadded,overflowcannotoccur.•Iftwonumbersofthesamesignareadded,overflowhasoccurredifandonlyiftheresultisoftheopposite•sign.

1.7.1.2 SubtractionAddition has the property of being commutative, that is, a+b = b+a. This is not true of subtraction. 5 – 3 is not the sameas3–5.Forthisreason,wemustbecarefuloftheorderoftheoperandswhensubtracting.Wecallthefirstoperand, the number which is being diminished, the minuend; the second operand, the amount to be subtracted from the minuend, is the subtrahend. The result is called the difference. 51 minuend– 22 subtrahend 29 difference

It is possible to perform binary subtraction using the same process we use for decimal subtraction, namely •subtracting individual digits and borrowing from the left.This process quickly becomes cumbersome as you borrow across successive zeroes in the minuend. Further, it •doesn’t lend itself well to automation. Jacobowitz describes the “carry” method of subtraction which some of you may have learned in elementary •school, where a one borrowed in the minuend is “paid back” by adding to the subtrahend digit to the left. This means that one need look no more than one column to the left when subtracting.Subtraction can thus be performed a column at a time with a carry to the left, analogous to addition. This is a •processwhichcanbeautomated,butweareleftwithdifficultieswhenthesubtrahendislargerthantheminuendor when either operand is, signed.


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Since we can form the complement of a binary number easily and can add signed numbers easily, the obvious •answer to the problem of subtraction is to take the 2’s complement of the subtrahend, then add it to the minuend. That is 51–22 = 51+ (–22).Not only does this approach remove many of the complications of subtraction by the usual method, but it also •means special circuits to perform subtraction need not be built All that is needed is a circuit which can form the bitwise complement of a number and an adder.

1.7.2 MultiplicationA simplistic way to perform multiplication is by repeated addition. In the example below, we could add 42 to the product register 27 times. In fact, some early computers performed multiplication this way. However, one of our goals is speed, and we can do much better using the familiar methods we have learned for multiplying decimal numbers. Recall that the multiplicand is multiplied by each digit of the multiplier to form a partial product, and then the partial products are added to form the total product. Each partial product is shifted left to align on the right with its multiplier digit. 42 multiplicandx 27 multiplier 294firstpartialproduct(42X7) 84 second partial product (42 X 2) 1134 total product

Binary multiplication of unsigned (or positive 2’s complement) numbers works exactly the same way, but is even easier because the digits of the multiplier are all either zero or one. That means the partial products are either zero or a copy of the multiplicand, shifted left appropriately. Consider the following binary multiplication:

0111 multiplicandx 0101 multiplier0111 firstpartialproduct (0111X1) 0000 second partial product (0111 X 0) 0111 third partial product (0111 X 1) 0000 fourth partial products (0111 X 0)0100011 total product

Notice that no true multiplication is necessary in forming the partial products. The fundamental operations required are shifting and addition. This means we can multiply unsigned or positive integers using only shifters and adders.

1.7.3 DivisionAs with the other arithmetic operations, division is based on the paper-and-pencil approach we learned for decimal arithmetic. We will show an algorithm for unsigned long division that is essentially similar to the decimal algorithm we learned in grade school. Let us divide 0110101 (5310) by 0101 (510). Beginning at the left of the dividend, we movetotherightonedigitatatimeuntilwehaveidentifiedaportionofthedividendwhichisgreaterthanorequalto the divisor. At this point, a one is placed in the quotient; all digits of the quotient to the left are assumed to be zero. The divisor is copied below the partial dividend and subtracted to produce a partial remainder as shown below.

Now digits from the dividend are “brought down” into the partial remainder until the partial remainder is again greater than or equal to the divisor. Zeroes are placed in the quotient until the partial remainder is greater than or equal to the divisor, and then a one is placed in the quotient, as shown below.

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The divisor is copied below the partial remainder and subtracted from it to form a new partial remainder. The process is repeated until all bits of the dividend have been used. The quotient is complete and the result of the last subtraction is the remainder. This completes the division. The quotient is (1010)2 (1010) and the remainder is (11)2 (310), which is the expected

result. This algorithm works only for unsigned numbers, but it is possible to extend it to 2’s complement numbers. As with the other algorithms, it can be implemented using only shifting, complementation, and addition.Digital computers can perform arithmetic operations using only binary numbers. And hence the above section of binary arithmetic is the basic step of digital electronics.


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Summary

There are mainly four number systems mainly binary, octal, decimal and hexadecimal which have 2, 8, 10 and •16 digits respectively. But it is the ease in applications that decides which kind of number system should tie definedandused.Everycomputerusestwoormoreoftheabovementionednumbersystemssimultaneously.The binary number system has only two digits; 0 and 1. A binary digit is called bit. A binary number can be •converted into its equivalent octal, decimal and hex numbers as described in the text. And octal, decimal and hex numbers can be converted into equivalent binary umbers.The octal number system has 8 digits; 0 through 7. An octal number can be converted into its equivalent binary, •decimal and hex numbers and vice versa as described in the text.The hex number system has 16 digits; 0 through 9, A through F. As in the other systems, the hex numbers can •be converted as described in the text into their binary, octal and decimal equivalents and vice versa.It is possible to arrange sets of binary digits to represent numbers, letters of the alphabet or other information •by using a given code. Some of the important codes are BCD and ASCII codes. In the BCD code, each decimal digit is replaced by its 4-bit binary equivalent. Conversion of BCD code into its decimal equivalent and vice versa is quite easy. Therefore, it is quite often •used in computers.The ASCII code is the most widely used alphanumeric code. It is a 7-bit binary number-and has 2• 7 = 128 possible 7-bitbinarynumberswhicharequitesufficienttodescribethecapitalandsmalllettersofthealphabet,digits,punctuation marks and other symbols.The process of dividing a binary number is once again the same as followed in the decimal system.•

ReferencesNumber Systems and Codes• [Pdf] Available at: <http://www.inf.fu-berlin.de/lehre/WS00/19504-V/Chapter1.pdf> [Accessed 19 June 2013]Number Systems, Base Conversions, and Computer Data Representation• [Pdf] Available at: <http://www.eecs.wsu.edu/~ee314/handouts/numsys.pdf> [Accessed 19 June 2013]Das, S., 2010. A Complete Guide to Computer Fundamentals, Laxmi Publications, Ltd.•Meena, K., 2009. • Principles of Digital Electronics, PHI Learning Pvt. Ltd.2011. • Binary Numbers: Tutorial, [Video online] Available at: <http://www.youtube.com/watch?v=biqp0HjJmfk> [Accessed 19 June 2013].2011. • Binary, Hexadecimal, Octal conversion, [Video online] Available at: <http://www.youtube.com/watch?v=2UwxdCLFW70> [Accessed 19 June 2013].

Recommended ReadingGodse, A.P. & Godse, D.A., 2008. • Digital Logic and Design and Application, Technical Publications.Godse, A.P. & Godse, D.A., 2005. • Digital Systems, Technical Publications.Tokheim, 2004. • Digital Electronics Principles and Applications, Tata McGraw-Hill Education.

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Self Assessment

Aim of any number system is to deal with certain quantities which can be measured, monitored, ________________, 1. manipulated arithmetically, observed and utilised.

recordeda. storedb. readc. usedd.

Which of the following is not a common number system?2. Decimal systema. Tetra decimal systemb. Binary systemc. Octal systemsd.

What are binary digits abbreviated as?3. Bytesa. Giga bytesb. Bitsc. Nibbled.

The 2’s complement of a binary number is obtained adding 1 to the ________________ of this number.4. complementa. endb. beginningc. 1’s complement d.

Binary number can be converted into its decimal equivalent by simply adding ________________of various 5. positions in the binary number which has bit 1.

weightsa. numberb. tenc. twod.

A decimal number is converted into its binary equivalent by its repeated ________________ by 2.6. additiona. divisionb. multiplicationc. subtractiond.

Advantage of the octal number system is the ease with which any octal number can be converted into its 7. ______________equivalent.

decimala. hexb. binaryc. tetrad.


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Which digits are excluded from the octal number system?8. 1 and 2a. 0 and 1b. 7 and 8c. 8 and 9d.

What should be added to last group of 3 bits if the MSB side does not have 3 bits while converting numbers 9. from binary to octal?

Zeroa. Oneb. Twoc. Nined.

In subtraction number which is being diminished is called the minuend; the amount to be subtracted from the 10. minuend is the called the________________.

differencea. subtrahendb. subtractionc. minusd.

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Chapter II

Logic Gates

Aim


explain logic gates•

introduce truth tables•

explore the types of logic gates•

Objectives


classify logic gates•

enlist the features of logic gates•

definelogiccircuits•

Learning outcome


analyse the working of logic gates•

identify the types of logic gates•

understand truth tables•


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2.1 IntroductionDigital computers understand the language of 1s and 0s. This number system is also called as binary number system (bi means two). Note that the operation of digital circuits can be described in two corresponding voltage levels. The more positive level is denoted by high (H = 1) and the other is denoted by low (L = 0). And the logical operations are represented by true (T) and false (F). For instance, H = 1 = T and L = 0 = F is a positive logic whereas H = 0 = F and L = 1 = T is a negative logic.

A digital circuit having one or more input signals but only one output signal is called “a gate”. A gate, which implements Boolean algebraic equations, is called “Logic gates”.

The basic building blocks of digital electronics are logic gates which perform simple binary logic functions (AND, OR, NOT, etc.). From these devices, more complex circuits can be constructed to do arithmetic, that act as memory elements.

2.2 Logic GatesFeatures of logic gates are as follows:

Theflowofdigitalsignalsiscontrolledbytransistorsinvariousconfigurationsdependingonthelogicfamily.•For most purposes we can imagine that the logic gates are composed of ideal switches with just two states: OPEN and CLOSED. The state of a switch is controlled by a digital signal. The switch remains closed so long as a logical (1) signal is applied. A logical (0) control signal keeps it open.Logicsignalsinteractbymeansofgates.ThethreefundamentalgatesAND,OR,andNOT,arenamedafter••the three fundamental operations of logic that they carry out. The AND and OR gates each have two inputs and one output. The output state is determined by the states of the two inputs.Thefunctionofeachgateisdefinedbyatruthtable,whichspecifiestheoutputstateforeachpossiblecombination•of input states. The output values of the truth tables can be understood in terms of two switches. If the switches are in series, you get the AND function. Parallel switches perform the OR operation. A bubble after a gate or at an input indicates NOT.ThethreecompoundgatesNAND,NORandXORcanbemadefromAND,OR,andNOT.NANDmeans••an AND gate followed by a NOT, while NOR means an OR gate followed by a NOT. The EXCLUSIVE-OR (XOR) is similar to OR but it has a LO output if both inputs are HI, so you can think of it as one OR the other but NOT both. NAND and NOR are more common than AND and OR because with the help of DeMorgan’s theorems they can be used to simplify complex circuits.When several gates are combined to perform a complex logical operation, a good design uses as few as possible. •Boolean algebra, the mathematics of two valued variables, is the theoretical tool used to simplify complex logical expressions.

2.2.1 NOT GateThe NOT gate has a single input and a single output and its symbol and truth table (truth table contains a table of all possible input values and their corresponding outputs values). It performs the operation of inversion, i.e., the output of a NOT gate takes a 1 (high) state if the input takes the 0 (low) state and vice-versa. A circuit, which performs a logic negation, is called a NOT circuit or inverter since it inverts the output with respect to the input.

2.2.2 OR GateThe OR gate has two or more inputs and a single output. The output of an OR gate is in 1 state if any of the inputs is in the 1 state.

2.2.3 AND GateThe AND gate has two or more inputs and a single output. The output of an AND gate is in 1 state if all inputs are in the 1 state or the output will be zero if any of the inputs is zero.

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2.2.4 NAND Gate

The Negated AND, NOT AND or NAND gate is the opposite of the digital AND gate, and behaves in a manner ••thatcorrespondstotheoppositeofANDgate,asshowninthetruthtable.ALOWoutputresultsonlyifboththe inputs to the gate are HIGH. If one or both inputs are LOW, a HIGH output results. The NAND gate is a universal gate in the sense that any Boolean function can be implemented by NAND gates.Digital systems employing certain logic circuits take advantage of NAND’s functional completeness. In •complicated logical expressions, normally written in terms of other logic functions such as AND, OR, and NOT, writing these in terms of NAND saves on cost, because implementing such circuits using NAND gate yields a more compact result than the alternatives.NAND gates can also be made with more than two inputs, yielding an output of LOW if all of the inputs are •HIGH, and an output of HIGH if any of the inputs is LOW.

2.2.5 NOR GateA contraction of NOT and OR, a NOR gate is one of the basic digital logic gates. With it, it is possible to build any of the other basic logic gates and thus, nearly any type of digital circuit.

2.2.6 XOR GateAbbreviated, XOR is a unique and very useful type of gate. As shown in the truth table, any time both of its inputs are held in the same state (either low or both high), its output will be low. If one of the inputs is pulled high while the other is held low, then its output will be high.

2.2.7 XNORXNOR is a digital logic gate whose function is the inverse of the Exclusive OR (XOR) gate. The two-input versions implement logical equality, behaving according to the truth table. A high output results if both of the inputs to the gate are the same. If one but not both inputs are high, a low output results.

Operation Switches Condition that Boolean Symbol Truth Table circuit is closed Notation

A

A

B

B

Series(A AND B are

closed)A • B or

ABA

A

A ᾹᾹᾹ

B

B

A-B

A+B

AND

AND

NOT(same as invert)

Differentkind of switch

1 means open0 means closed

NOT A =

Paralle

(A OR B is closed) A+B

A B0 00 11 01 1A B0 00 11 01 1

01

10

0111

0001

A+B

A •B

A

(a)

NAND

NOR

XOR

X-NOR gate

InputA

InputB

Output

A

A

A

B

B

B

A - B

A +B

A B+

= AB + AB


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(b)

A B Output0 0 10 1 11 0 11 1 0

NAND

A B Output0 0 10 1 01 0 01 1 0

NOR

A B Output0 0 00 1 1 1 0 1 1 1 0

XOR

A B Output0 0 00 1 11 0 11 1 0

XNOR

(c)Fig. 2.1 Logic gates (a) Basic logic gates; (b) Compound logic gates (c) Truth tables for compound gates(Source:http://www.beam-wiki.org/wiki/NOR;http://www.pdf-finder.com/Digital-Electronics-I:-Logic,-Flip-

Flops,-and-Clocks.html).

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2.3 Truth TablesTruth tables are used to show logic gate functions. The NOT gate has only one input, but all the others have two inputs.

When constructing a truth table, the binary values 1 and 0 are used. Every possible combination, depending on number of inputs, is produced. Basically, the number of possible combinations of 1s and 0s is 2n where n= number of inputs. For example, 2 inputs have 22 combinations (i.e. 4), 3 inputs have 23 combinations (i.e. 8) and so on. The next section shows how these truth tables are used.

2.3.1 Description of the six logic gates

NOT gate•

A XNOT XA

Fig. 2.2 Not gate(Source: http://education.cambridge.org/media/577240/cambridge_igcse_computer_studies__revision_guide___

cambridge_education___cambridge_university_press_samples.pdf)

INPUT A OUTPUT X0 11 0

Truth table

The output (X) is true (i.e. 1 or ON) if: INPUT A is NOT TRUE (i.e. 0 or OFF) Truth table for: X = NOT A

AND gate•

X XAND

AA

B B

Fig. 2.3 AND gate(Source: http://education.cambridge.org/media/577240/cambridge_igcse_computer_studies__revision_guide___



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INPUT A INPUT B OUTPUT X0 0 00 1 01 0 01 1 1

Truth table

The output (X) is true (i.e. 1 or ON) if: INPUT A AND INPUT B are BOTH TRUE (i.e. 1 or ON) Truth table for: X = A AND B

OR gate•

XA

BXOR

A

B

Fig. 2.4 OR gate(Source: http://education.cambridge.org/media/577240/cambridge_igcse_computer_studies__revision_guide___



Truth table

The output (X) is true (i.e. 1 or ON) if: INPUT A OR INPUT B is TRUE (i.e. 1 or ON) Truth table for: X = A OR B

NAND gate•

X

A A

B B

XNAND

Fig. 2.5 NAND gate(Source: http://education.cambridge.org/media/577240/cambridge_igcse_computer_studies__revision_guide___


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Truth table

The output (X) is true (i.e. 1 or ON) if: INPUT A AND INPUT B are NOT BOTH TRUE (i.e. 1 or ON) Truth table for: X = NOT A AND B

NOR gate•

A

BXNOR

A

B

X

Fig. 2.6 NOR gate(Source: http://education.cambridge.org/media/577240/cambridge_igcse_computer_studies__revision_guide___



Truth table

The output (X) is true (i.e. 1 or ON) if: INPUT A OR INPUT B are NOT BOTH TRUE (i.e. 1 or ON) Truth table for: X = NOT A OR B

XOR gate••

X

A A

B BXXOR

Fig. 2.7 XOR gate(Source:http://education.cambridge.org/media/577240/cambridge_igcse_computer_studies__revision_guide___

cambridge_education___cambridge_university_press_samples.pdf).


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Truth table

The output (X) is true (i.e. 1 or ON) if: INPUT A OR (NOT INPUT B) OR (NOT INPUT A) OR INPUT B is TRUE (i.e. 1 or ON) Truth table for: X = A OR (NOT B) OR (NOT A) OR B

2.4 Logic circuits/networksLogic gates can be combined together to produce more complex logic circuits (networks). A key point to be taken into account is the output from a logic circuit (network) is checked by producing a truth table.

Two different types of problems are considered here:drawing the truth table from a given logic circuit (network)•designing a logic circuit (network) from a given problem and testing it by also drawing a truth table.•

Example 1Produce a truth table from the following logic circuit (network).

CAND

NOR

OR X

A

B

P

Q

To show how this works, we will split the logic circuit into two parts (shown by the dotted line).

Fig. 2.8 Logic circuit(Source: http://education.cambridge.org/media/577240/cambridge_igcse_computer_studies__revision_guide___cambridge_education___cambridge_university_press_samples.pdf)

First partThere are 3 inputs; thus we must have 23 (i.e. 8) possible combinations of 1s and 0s.Tofindthevalues(outputs)atpointsPandQ,itisnecessarytoconsiderthetruthtablesfortheNORgate(outputP) and the AND gate (output Q) i.e.P = A NOR BQ = B AND C

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We thus get:INPUT A INPUT B INPUT C OUTPUT P OUTPUT Q

0 0 0 1 00 0 1 1 00 1 0 0 00 1 1 0 11 0 0 0 01 0 1 0 01 1 0 0 01 1 1 0 1

Truth table

Second partThere are 8 values from P and Q which form the inputs to the last OR gate.Hence we get X = P OR Q which gives the following truth table:

INPUT P INPUT Q OUTPUT X1 0 11 0 10 0 00 1 10 0 00 0 00 0 00 1 1

Truth table

Thisnowgivesusthefinaltruthtableforthelogiccircuitgivenatthestartoftheexample:

INPUT A INPUT B INPUT C OUTPUT X0 0 0 10 0 1 10 1 0 00 1 1 11 0 0 01 0 1 01 1 0 01 1 1 1

Truth tableExample 2Consider the following problem.A system used 3 switches A, B and C; a combination of switches determines whether an alarm, X, sounds: If switch A or switch B are in the ON position and if switch C is in the OFF position then a signal to sound an alarm, X is produced. It is possible to convert this problem into a logic statement.


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So we get:If (A = 1 OR B = 1) •

Thefirstpartistwoinputs(AandB)joinedbyanORgate.AND•

TheoutputfromthefirstpartandthethirdpartarejoinedbyanANDgate.(C = NOT 1) then X = 1•

The third part is one input (C) which is put through a NOT gate.So we get the following logic circuit (network):

AND

OR

X

A

B

C

Fig. 2.9 Logic circuit(Source: http://education.cambridge.org/media/577240/cambridge_igcse_computer_studies__revision_guide___


This gives the following truth table:

INPUT A INPUT B INPUT C OUTPUT X0 0 0 00 0 1 00 1 0 10 1 1 01 0 0 11 0 1 01 1 0 11 1 1 0

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Example 3A manufacturing process is controlled by a built in logic circuit which is made up of AND, OR and NOT gates only. The process receives a STOP signal (i.e. X = 1) depending on certain conditions, shown in the following table:

INPUT BINARY VALUES CONDITION IN PROCESS

V 1 Volume> 1000 litres

V 0 Volume≤1000liters

T 1 Temperature > 750 degrees Celsius

T 0 Temperature≤750degreesCelsius

S 1 Speed > 15 meters/second (m/s)

S 0 Speed≤15meters/second(m/s)

Table 2.1 Truth table

A stop signal (X = 1) occurs when: either Volume, V > 1000 litres and Speed, S <= 15 m/s or Temperature, T <= 750ºC and Speed, S > 15 m/sDraw the logic circuit and truth table to show all the possible situations when the stop signal could be received. First of all, it is necessary to turn the problem into a series of logic statements:

statement 1 can now be re-written as:•V = 1 AND S = NOT 1 since V > 1000 (binary value = 1) and S <= 15 (binary value = 0)

statement 2 can now be re-written as:•T = NOT 1 AND S = 1 since T <= 750ºC (binary value = 0) and S > 15 (binary value = 1)

both statements are joined together by an OR gate•

So, our logic statement becomes:X = 1 if (V = 1 AND S = NOT 1) OR (T = NOT 1 AND S = 1)We can now draw the logic circuit (network) by constructing it for statement 1 and for statement 2 and joining them with an OR gate.

In the following logic circuit note that V has been placed at the bottom of logic diagram – this is done to avoid crossing over of lines which makes it look neater and less complex. It is not essential to do this and is only done for the reasons given.


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AND

AND

NOT

NOT

Statement 1

Statement 2

OR X

T

S

V

Fig. 2.10 Logic circuit(Source:http://education.cambridge.org/media/577240/cambridge_igcse_computer_studies__revision_guide___


We can now construct the truth table:

INPUT V INPUT T INPUT S OUTPUT X0 0 0 00 0 1 10 1 0 00 1 1 01 0 0 11 0 1 11 1 0 11 1 1 0

Truth table

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SummaryDigital computers understand the language of 1s and 0s.•A digital circuit having one or more input signals but only one output signal is called “a gate”.•Thefunctionofeachgateisdefinedbyatruthtable,whichspecifiestheoutputstateforeachpossiblecombination•of input states.Boolean algebra, the mathematics of two valued variables, is the theoretical tool used to simplify complex •logical expressions.A circuit, which performs a logic negation, is called a NOT circuit or inverter since it inverts the output with •respect to the input.Logic signals interact by means of gates.•A gate, which implements Boolean algebraic equations, is called “Logic gates”.•Digital systems employing certain logic circuits take advantage of NAND’s functional completeness.•ThethreefundamentalgatesAND,OR,andNOT,arenamedafter•thethreefundamentaloperationsoflogic•that they carry out.Logic gates can be combined together to produce more complex logic circuits (networks).•When constructing a truth table, the binary values 1 and 0 are used.•When several gates are combined to perform a complex logical operation, a good design uses as few as •possible.Theflowof digital signals is controlled by transistors in various configurations depending on the logic•family.The OR gate has two or more inputs and a single output.•A manufacturing process is controlled by a built in logic circuit which is made up of AND, OR and NOT gates •only.

ReferencesRafiquzzaman,M.,2005.• Fundamentals of Digital Logic and Microcomputer Design, 5th ed., John Wiley & Sons.Balabanian, N. & Carlson, B., 2007. • Digital Logic Design Principles, John Wiley & Sons.2012. • An Introduction to Logic Gates, [Video online] Available at: <http://www.youtube.com/watch?v=95kv5BF2Z9E> [Accessed 29 May 2013].2012. • Logical Gates, Part 1, [Video online] Available at: <http://www.youtube.com/watch?v=6s0AR3_-i0k>[Accessed 29 May 2013].Logic gates• [Pdf] Available at: <http://education.cambridge.org/media/577240/cambridge_igcse_computer_studies__revision_guide___cambridge_education___cambridge_university_press_samples.pdf> [Accessed 29 May 2013].Logic Gates• [Pdf] Available at: <http://ptgmedia.pearsoncmg.com/images/chap3_0130619701/elementLinks/chap3_0130619701.pdf> [Accessed 29 May 2013].

Recommended ReadingSaha, A. & Manna, N., 2009. • Digital Principles and Logic Design Engineering series, Jones & Bartlett Learning.Godse, A. P. & Godse, D. A., 2009. • Digital Electronics and Logic Design, Technical Publications.Godse, A. P. & Godse, D. A., 2009. • Digital Logic Circuits, Technical Publications.


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Self Assessment

What computers understand the language of 1s and 0s?1. Alla. Microb. Superc. Digitald.

A digital circuit having ___________or more input signals but only one output signal is called “a gate”.2. twoa. oneb. threec. fourd.

A circuit, which performs a logic negation, is called a ___________circuit or inverter since it inverts the output 3. with respect to the input.

NORa. ANDb. NOTc. ORd.

What are used to show logic gate functions?4. Truth tablesa. Logic gatesb. Binary valuesc. Digital systemsd.

Which of the following statements is true?5. Gate signals interact by means of logic.a. Logic signals cannot interact by means of gates.b. Binary signals interact by means of gates.c. Logic signals interact by means of gates.d.

Which of the following statements is true?6. A system, which implements Boolean algebraic equations, is called “Logic gates”.a. A gate, which implements Boolean algebraic equations, is called “Logic gates”.b. A digital system, which implements Boolean algebraic equations, is called “Logic gates”.c. A truth table, which implements Boolean algebraic equations, is called “Logic gates”.d.

What can be combined together to produce more complex logic circuits (networks)?7. Digital systemsa. Binary signalsb. Logic gatesc. Truth tablesd.

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Which gate has only one input, but all the others have two inputs?8. NOTa. ORb. ANDc. NORd.

___________switches perform the OR operation.9. Gatea. Logicb. Binaryc. Paralleld.

Match the following10.

AND gate1. It is a unique and very useful type of gate.A.

NOR gate 2. It performs the operation of inversionB.

XOR gate3. It is one of the basic digital logic gates.C.

NOT gate4. It has two or more inputs and a single output.D. 1-A , 2-C , 3-D ,4-Ba. 1-C , 2-D , 3-B , 4-Ab. 1-D , 2-C , 3-A , 4-Bc. 1-D , 2-A , 3-B , 4-Cd.


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Chapter III

Computer Components and Information Processing Cycle

Aim

The aim of the chapter is to:

explain the components of computer•

explicate the information processing cycle•

elucidate the secondary storage devices•

Objectives

The objectives of the chapter are to:

expain the role of various input devices•

explicate important stages of computer processing in the CPU•

enlist various output devices•

Learning outcome

After end of this chapter, you will be able to:

understand the features of central processing unit•

describe various types of output devices•

identify secondary storage devices•

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3.1 IntroductionThefirstchapterdescribedhowdataisrepresentedforcomputers.Dataintheformofbinarydigitsisusedbythecomputer to give desired results. But how does the computer receive and use the data, how it is processed, how are the results generated and conveyed?

Tounderstandtheinformationprocessingcycleofacomputer,wefirstneedtostudyaboutthepartsorcomponentsof a computer.

3.2 ComponentsAs with most products, computers are designed in a variety of ways. There are, however, major similarities regardless of the brand (e.g. Dell, Gateway, IBM) of the computer. A computer system accepts data as an input: processes that data and provides data as output. During the processing the data must be stored. The processing is controlled by a sequence of instructions - the program - which is stored in the computer. The basic components of a computer system arethereforeinputdevices,processor,backingstoragedevicesandoutputdevices.Thisfittogetherasdepictedinthefollowingfiguresasaschematicrepresentation,aswellastheactualrepresentationofacomputer.

Fig. 3.1 Schematic representation of a computer system (Source: http://www.egyankosh.ac.in/bitstream/123456789/985/1/Unit%201.pdf)

3.3 Input DevicesThe computer needs an input in some form to proceed with the next steps. Input and output devices are collectively called I/O devices. Input devices (and also output devices) are the hardware interfaces between the human user and computer system, but (as always) hardware is ‘driven’ by software, so when we talk about an I/O device, remember there is an associated ‘device driver.’

3.3.1 Keyboard

Keyboard is the most common data entry device having more than 100 keys on it. Almost all general-purpose •computers are supplied with a keyboard.When you press a key, a number (code) is sent to the computer to tell it which key you have pressed. Keyboards •are often used in conjunction with a screen on which the data entered are displayed. The keys on a keyboard are usually arranged in the same order as those on a typewriter. This layout of keys is called •QWERTYbecauseQ-W-E-R-T-Yistheorderinwhichthelettersoccuronthetoprowofthekeyboard.

INPUTKeybord

Digitizer (e.g. mouse)Sorcon

OUTPUTVideo (Screen)

Audio (Speaker)Printer/Plotter

SECONDARYSTORAGEDiskette, Hard Disk, Optical*

PRIMARYSTORAGE(RAM and ROM) COMMUNICATIONS

Telecommunications (modem)Networks: Direct Connections

CONTROL UNIT (CU)

ARITMETIC LOGIC UNIT (ALU)

CPU


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Keyboards arewidely used because they provideflexiblemethod of data entry and can be used inmost•applications. However, they do have limitations like entry using keyboard is a slow form of data entry process and is prone to error.

3.3.2 Pointing DevicesThese are also called Cursor Control Devices. Cursor Control Devices are used to place the cursor (a highlighted screen location indicating where the next action will occur), select menu items, and control the computer by ‘clicking buttons’ on the screen. If these are built into the computer they are called Integrated Pointing Devices. A few such devices available are:

Mouse: A standard device of GUI (Graphical User Interface). New versions are optic and have no moving parts. •AnLED(LightEmittedDiode)recordsareflectedlightwhichsensesmotionoveraflatsurface.Trackballs: Like an ‘upside-down mouse’: it has the advantage of being stationary.•Joysticks: A hand-held stick that pivots about one end indicating 360 degree directions.•Trackpointorpointingstick:Aminiaturejoystickthatrespondstothetouchofasinglefinger.•Trackpads:Atouchsensitivesurfacethattranslatesfingermotionintocursormotion.•

3.3.3 Pen Input DevicesThese are based on screens that sense the location of a special pen that is connected to the terminal. Following are some of the devices:

Light pens either detect the monitor’s light or emit light that can be picked up by a specially designed •monitor.Styluses are pens with electronic point heads which activate pixels on the monitor, usually a LCD display.•Handwriting recognition software translates alphanumeric to digitised equivalents: normally these needs to be •‘trained’ to recognise an individual’s carefully printed letters, numbers, and symbols. These have been rather primitive,butsignificantadvanceshavebeenmaderecently.Theyaretheprimaryinputdeviceofhand-heldPDAs (Personal Digital Assistants) and PIMs (Personal Information Managers) state –of-the- art readers reportedly are very accurate.Digitizing tablets are similar to light pens or styluses except one draws on a tablet rather than the screen. •Touch screen recognises human touch and allows selection of menu items displayed on a monitor by touching •them.

3.3.4 Video Input DevicesFollowing are the various video input devices:Digital cameras

Digital cameras have optics like regular photographic cameras: however, they record the single images •electronically(ratherthanonphotographicfilm)indigitalform.Theseimagesarestoredincamera’sRAM(Random Access Memory), which like that in a computer is volatile. The images can be displayed immediately or stored on a secondary storage medium, e.g. a diskette, and processed •later using image processing software.

Digital video camerasThese are digital cameras which can store sequences of digital images on magnetic tape and play them back as •‘movies.’ They are similar to camcorders, but camcorders store their images as analogue data. Digital video cameras are essential features of video conferencing where remote computers can actually control •a remote camera and remote users can share applications and collaborate on ‘whiteboards.’

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Analogue image convertersPhotographs taken with regular cameras and videos recorded with camcorders store their images as analogue •data. There are special kinds of hardware that can take these images (scanning photographs or converting camcorder •tapes) and convert them to digital images which, like any other digital image, can be processed by computers.

3.3.5 Audio Input DevicesFollowing are the various audio input devices:Digitized audio signals

Audio (analogue) signals can be converted to digital signals by analogue to digital converters, processed by a •computer and converted back with digital to analog converters. This allows computer manipulation of music (See MIDI, below), speech or any recordable sounds.Synthetic audio signals can be created by the computer. •Musical Instrument Digital Interface (MIDI) devices allow the input and output to any musical instrument •capable of electrical I/O. The music, once digitised in the computer’s memory can be processed by musical software giving incredible opportunities for creativity and innovation.

Voice input and speech recognitionMicrophones convert spoken words (analog signals) to digital signals that can be processed by a computer. •(Words are ‘digitised’)Digitized words are compared to ‘voice templates’ stored in memory.•

Customisable devices can be ‘trained’ to recognise an individual’s speech �Current systems are still rather primitive and have limited vocabularies: however, rapid developments are �being reported.

If a word is recognised, it is processed: if not, then the user has to give a recognisable input.•

3.3.6 Graphic Capture DevicesImage scanners are popular examples of graphic capture devices. When a page of text already exists, like the page that you are reading now, it can be directly put into a computer using a scanner. Scanner can be used to input not only the texts, but also the photographs, drawings and so on. Image Scanners (Gray-scale or colour) digitize the pictures(whichareanalogdata).Theresultingbitmappedimages(Eachpixelhasacollectionofbitsthatdefineitscolour)canbeeasilymodifiedbygraphicsprograms.Theresolutionofbitmappedimagesismeasuredindpi,i.e.,dots per inch.

3.3.7 Code NumbersBarcode readers

The bar code is a pattern of thick and thin bars divided by thick and thin spaces. Only the relative separations •and thickness of the bars are important. Barcodes can be printed in different sizes and colours. The barcode is read either by passing a light-pen over it •orbypassingthebarcodeoveraflatbedscanner.Barcodes are suitable for data input when all that is necessary is to identify an item, and the data input simply •comprises a code. The reading of the barcode records a transaction, and information is fed back to a computer database. Barcode •systems are easy to operate and have very low error rates.Occasionally, a scanner can read a barcode number incorrectly. A check digit is included in the barcode number •to reduce such incidents.


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Magnetic ink character recognition (MICR)This input device is widely used by banks to process the tremendous volume of checks being received by •them. This can be seen at the bottom of a check leaf, where some code numbers are written using a special ink that •contains magnetisable particles of iron oxide.

Magnetic stripe codeIt is a short length of magnetic tape which may be stuck on the surface of a tag, card or document. On plastic •cards such as credit cards, the stripe is usually sealed in. Stripes store data in the form of magnetic spots which represent the 1’s and 0’s of the ASCII code.•

Smart cardsThese have a memory store in the form of a very thin integrated circuit sealed into them.•These can be used to store data about a customer, which can be updated as transactions are made using the •card.

3.3.8 Optical Input DevicesFollowing are the optical input devices:Optical Character Readers (OCR)

This device is similar in concept to MICR. Characters in a special font are printed on a document, and the reader •scansthedocumentforreflectedlightpatterns,thentranslatesthosepatternsintoapatternofelectricalsignals,which are passed to the computer store.

Optical Mark Readers (OMR)These are similar to OCR except that the reader recognises marks in appropriately positioned boxes rather than •characters. These are found in areas where responses are one out of a small number of alternatives and the volume of data •to be processed is large. One can notice the usage OMR in bank examinations.

3.4 Central Processing UnitThe data given as an input to the computer is then processed at the Central Processing Unit (CPU). It can be thought of as a collection of processing and storage units within an Arithmetic Logic Unit (ALU) and Control Unit (CU) that are linked internally and externally by busses which carry binary signals between. Higher the bandwidth or processing speed of CPU the faster the machine is.

3.4.1 Arithmetic Logic Unit (ALU)The Arithmetic Logic Unit (ALU), as the name indicates, performs all the arithmetic and logic operation. ALU consists of:

Accumulator: It is the main data register where all the intermediate results of a calculation are kept (accumulated) •untilthefinalresultisdetermined(whichisthenstoredinmemory).Data registers are supplemental storage registers that support the operations of the accumulator.•Computational circuits (e.g. a binary adder) performs mathematical operations.•Operational circuits that perform logic operations: Here, all math operations are performed in binary numbers •and all logic operations are performed using binary operations. Math operations include addition, subtraction, multiplication and division. Logical operations allow programs to contain repetition and selection, the two essential control structures of programming. Logical operations performed by ALU include comparing two quantities: keeping a counter and deciding the further route.

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3.4.2 Control Unit (CU)This unit controls the internal functioning of a computer and input/output units. The role of control unit in CPU isthatofa‘manager’or‘atrafficcop.’Inotherwords,itcontrolsandco-ordinatesallhardwareoperations.ThecomponentsofCU(greatlyoversimplifiedforillustrativepurposes)are:

Decoders interpret program instructions (object code written in machine language).•Timer (or clock) sequences all CPU activities.•Logical gates and circuits distribute signals which activate various components of the CPU.•Program counter/register keeps track of the next instruction to be executed•Registers is a group of (usually) bistable devices that are used to store information like instructions, address •and so on, within a computer system for high-speed access.

Primary CU Functions of primary CU are:

Read and interpret machine language instructions•Control the transmission of data between ALU, registers, cashes, primary memory, and auxiliary memory•Control the sequence of execution of program instruction (i.e. govern branching, jumping around within a •program) which allows repetition and selectionDirect ALU as to what math or logic operations to perform.•

3.4.3 Primary Memory

Primary memory, also called main memory or internal memory, provides temporary storage of programs in •execution and the data being processed. It is known as Immediate Access Storage (IAS) as this is the portion of CPU which can be accessed directly. •From the hardware point of view, the primary memory is formed by a large number of basic units referred to as •‘memory cells.’ Each memory cell is a device or an electronic circuit that has two or more stable states, which represents the binary numbers 0 (Zero) or 1 (One). The computer can retrieve any item of data or any instruction stored in primary memory at lightning speed. The •modern computer does this in a few nano seconds. Primary memory can be further grouped into Random Access Memory (RAM) and Read Only Memory (ROM). •Cache memory (small, fast RAM) is designed to hold frequently used data. Summary of the features of each as given below:

Random Access Memory (RAM)This memory allows writing as well as reading of data, unlike ROM on which data cannot be written. •It is a volatile storage because the contents of RAM are lost when the power (computer) is turned off. If you •want to store the data for later use, you have to transfer all the contents to a secondary storage device.

There are several types of RAM, the most popular of which include:Dynamic RAM (DRAM), although its name sounds sophisticated, is the oldest and simplest (and therefore �the slowest) type of RAM used today. The word ‘dynamic’ comes from the fact that it must be electronically ‘refreshed’ constantly in order to maintain the stored data.StaticRAM(SRAM),unlikeDRAM,doesnotneedtoberefreshed:itsstorageisfixed(aslongaspower �is supplied to the computer). This newer, more dependable, type of RAM is faster but more expensive than DRAM. SRAM is often used for cache memory.Enhanced Data Output DRAM (EDO RAM) is a type of RAM that improves the memory access time on faster �microprocessors such as the Intel Pentium. EDO RAM was initially optimised for the 66 MHz Pentium. Synchronous DRAM (SDRAM) is a new form of RAM that can be synchronised to the clock speed of the �computer, a powerful feature that optimises data access by the system buses.


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Ram bus DRAM (RDRAM) is Intel’s designated successor to SDRAM having an effective speed of 800 MHz �and a peak data transfer rate of 1.6 GBps. However, it has yet to prove itself, and there are several rivals, e.g. DDR SDRAM, that are slower but have 64b bus widths thus providing comparable transfer rates.

Read Only Memory (ROM)Another type of microcomputer memory is read only memory. Data is ‘burnt’ into the ROM chip at the time •of manufacturing. Unlike RAM, the data on the ROM is non-volatile, i.e. data is not lost when the computer is switched off. •

Following are the popular ROMs:Programmable ROM (PROM) can be programmed to record information using a facility known as a PROM- �programmer. Once the chip has been programmed, the recorded information cannot be changed. Erasable PROM (EPROM) is erased by shining ultraviolet light on the exposed chip. To write to or erase �from EPROM, one must use a PROM burner.Electronically Erasable PROM (EEPROM) is more convenient than EPROM, because it can be erased �electronically and can be written to in bytes.Flash Memory, a special type of EEPROM, can be erased and rewritten in multi-byte blocks rather than the �single bytes characteristic of EEPROM. Flash memory is most often used to hold control code such as the BasicInput/outputSystem(BIOS)inapersonalcomputer:theseareoftencalled‘flashBIOS’.

Cache Memory (small, fast RAM)It is designed to hold frequently used data. In general, • Cache(highspeedRAMthatisconfiguredtoholdthemost frequently used data) is used to improve system performance.Memory cache or CPU cache is a dedicated bank of high-speed RAM chips used to cache data from primary •memory. When data is read from primary memory, a block larger than immediately necessary is stored in the cache under •the assumption that the next data needed by a program will be located near the data being read: when that data is needed, it will then be waiting in the high speed cache. Memory Cache may be either built into the CPU (level 1, or L1, cache, e.g. Pentiums and PowerPCs) or contained •in separate chips (level 2, or L2, cache,).After the data received through the input devices is processed in the central processing unit, the data in the form •of result is dispatched through the output devices.

3.5 Output DevicesOutput devices are the means by which computer systems communicate with people. Output devices accept data from the processor and convert them into the required output format. The convenience of use of these devices and thequalityoftheirresultshasasignificantimpactontheeffectivenessofacomputersystem.Inotherwords,outputdevices translate the data in the processor into a format that is suitable for people to use. Most ‘real world’ data is analogue, i.e. it consists of continuous signals like sounds, pictures, voltage and so forth.

However, computers can only process digital data (discrete signals): therefore, input usually involves analogue to digitalconversion(A/Dhardware)andoutputreversestheprocessusingD/Aconverters.Outputcanbesub-classifiedas either direct (to/from I/O devices) or indirect (to/from secondary storage). Output can also be divided into another twokinds:hardcopyoutput(paper,microfilm,etc.)providesapermanentrecordwhilesoftcopyoutput(visual,audio, tactile, or action) is transient. Action output facilitates control of electromechanical devices, e.g. robotics. Forthesakeofconvenience,letusfollowthegivenclassificationtodiscusstheoutputdevices.

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3.5.1 Visual Output Devices (Soft copy)

Cathode Ray Tube Displays (CRTs)•These are the most commonly seen output device. The computer screen is made of CRTs. They are also �called monitors or visual display terminals (VDTs). Monitors look identical to a television screen. They produce fast and virtually costless output of �information.CRTs use faster scan technology to portray images as bitmapped graphics on a phosphorescent screen. �Electronsarefiredatthescreenandlightuptinydotsofphosphor,whichthenglowforashortperiodoftime. Each point is called a picture element or pixel. Sincethephosphorsglowmomentarily, theelectronicgunkeepsonfiringtheelectronbeamatregular �intervals. This refreshing mechanism is measured in Hertz (Hz) or cycles per second. A low refresh rate leadstoscreenflicker.Monochrome monitors use one colour images (usually black) on a one colour background (usually white), �e.g. old mainframe monitors. These are now virtually obsolete in PCs.On the other hand, colour monitors use a triad of red, green, and blue phosphor dots which are stimulated �in varying degrees to produce a wide range of colours. Composite video monitors (like TVs) have one electron gun. However, composite video has lower resolutions �than RGB monitors. RGB monitors use three electron beams which give a higher resolution display. Virtually, all modern monitors are RGB.The quality of the screen display or its resolution depends on the number of pixels on the screen. Resolution �indicates the ability to show details: the more pixels per inch, the higher the resolution.

Bitmapped CRTs allows individual pixels to be addressed thereby producing greater screen control: this is •theoriginofWYSIWYG(WhatYouSeeIsWhatYouGet)applicationsthatcanincorporatehighresolutiongraphics (e.g. all modern PC monitors).On the other hand, old fashioned character-addressable CRTs only address or manipulate groups of pixels •(thatformalphanumeric)andareinherentlynon-WYSIWYGandhavecrudegraphics(e.g.mainframeandminicomputer monitors). VectorGraphicsscreenscreateimagesbytheelectronguntracingbetweenspecifiedpointsonthescreenrather•than scanning every row: they are limited to special types of graphics monitors.FlatPanelDisplay,firstintroducedinwatchesandclocksin1970s,isatechnologynowappliedtodisplay•terminals.TheyeliminateflickerandradiationandminimisesizeproblemsofCRTs.Further,theyarepopularfortheir low energy consumption. However, the quality of the images is relatively poor. Hence, they are commonly used in portable devices because of compactness and low energy requirements.Liquid Crystal Display (LCD) is the most popular type, which has a thin layer of liquid crystal molecules divided •into small squares forming pixels that are held by two glass sheets. When power is applied to a square it turns opaque.LCDsusedtocomeinlimitedsize,brightnessandclarity,butcurrenttechnologyhassignificantlyimproved. Gas-plasma displays give the best image (though low contrast), but they cannot be battery operated.•Project Display is a small sized screen of the displays discussed above. Project displays provides an enlarged •image and could be projected on a large screen. These systems can be connected directly to the processor and the output will be displayed on the large screens.

3.5.2 Audio Output Devices (Soft copy)

The audio output device converts the digital signals and gives the output in an audible format. • Speech synthesisers transform digital computer signals into voice output. The voice maybe choppy and unnatural, but it is easily understood. Audio output units have a varied application.Speech synthesizers use different methods of output. In the • word analysis method, entire digitised words from the computer’s vocabulary are combined under computer control, into digitised sentences and then converted to analogue output. This requires a huge amount of memory.


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In the • constructive synthesis method, the basic elements of speech, called ‘phonemes’ (only 40 in the English language)areusedtoconstructspeechoutputgovernedbytiming,pitchandinflectioncontrols.Thishasminimalmemory requirements.

3.5.3 Hardcopy Devices (Print and Film)Printers and PlottersPrintersThese are used to print the output data on paper. Such output is referred to as printout or hard copy. Printers can be classifiedasfollows,basedonvariouscharacteristics:

Image Formation (measured in dpi):•Full character alphanumeric (no graphics) have a separate symbol on a ball, daisy wheels, thimble, band, �belt or chain mechanism.Dot-matrix alphanumeric and graphics are formed by patterns of dots from a single print head. �Raster scan images (alphanumeric/graphics), e.g. laser printers, are like copiers. �

Image Transfer•Impact printers transfer images by, the print head striking a ribbon like a typewriter. �Non-impact printers transfer images by heat (electro-thermal and thermal-transfer printers), electrostatic �charge (laser printers), or by ‘drawing’ with ink jets.

Number of characters printed at one time, measured in ppm (pages per minute):Serial (bi-directional) printers print one alphanumeric or graphics pixel at a time. �Chain printers transfer one line of alphanumeric or pixels at a time. �Page printers (laser printers) utilise a combination of raster scan and xerographic technologies to produce �one whole page at a time.

PlottersThough a few printers listed above are capable of producing graphics, there are a few special plotters exclusively to print a good quality drawing and graphs. There are two types of plotters:

Flatbed plotters have a drawing instrument (pen, ink-jet, electrostatic head, or heater element) that moves both •horizontallyandvertically,underthecontrolofinputvoltages,overaflatpieceofstationarypaper.Drum plotters have a drawing pen that move vertically, while the paper on a drum rotates under it.•

3.5.4ComputerOutputMicrofilms(COM)

Specialcomputerscanproducetheiroutputdirectlyontomicrofilm.Inthisway,vastamountsofdatainhuman•readable form can be stored in a very small space without the need of large quantities of paper. Themicrofilmisreadbyusingaspecialdevicewhichmagnifiesthetextandpicturessothattheycanbeseen•with naked eyes.

3.6 Data StorageStorage refers to the media and methods used to keep information available for later use. Some things will be needed right away while other won't be needed for extended periods of time. Therefore different methods of storage are appropriate for different uses. The RAM, ROM, earlier described as a part of CPU, is the main memory of a computer. Main memory keeps track of what is currently being processed. These memory chips are the fastest, but most expensive, type of storage. It is volatile, meaning that turning the power off erases all of the data.

3.6.1 Auxiliary Storage/Secondary StorageAuxiliarystorageholdswhatisnotcurrentlybeingprocessed.Thisisthepartthatis‘filedaway’,butisreadilyavailable when needed. It is non-volatile, meaning that turning the power off does not erase it.

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The primary storage has already been discussed: the secondary storage devices are as follows.

3.6.2 Magnetic Disk

A magnetic disk is a circular platter of plastic, which is coated with magnetised material. One of the key •components of a magnetic disk is a conducting coil named as Head (Read-write head) which performs the job of reading and writing on the magnetic surface. The head remains stationary while the disk rotates below it for reading or writing operation. All magnetic disks are similarly formatted, or divided into areas called tracks, sectors and cylinders.•Disk sector is a wedge-shape piece of the disk, shown in grey. Each sector is numbered. •

Fig. 3.2 Disk sectors(Source: http://www.jegsworks.com/Lessons/lesson6/lesson6-3.htm)

Fig. 3.3 Track sectors(Source: http://www.jegsworks.com/Lessons/lesson6/lesson6-3.htm)

A track sector is the area of intersection of a track and a sector, shown in grey.•The head of disk is a small coil and reads or writes on the position of the disk rotating below it: therefore, the •data is stored in concentric set of rings called tracks. The width of a track is equal to the width of the head. To minimisetheinterferenceofmagneticfieldsandtominimisetheerrorsofmisalignmentofhead,theadjacenttracks are separated by inter track gaps. As we go towards the outer tracks, the size of a track increases but to simplify electronics same numbers of bits are stored on each track


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DiskPlatter

Inter Sector gapor Intra track gap

Intra track gap

Sector

Fig. 3.4 Logical layout of magnetic disk(Source: http://www.egyankosh.ac.in/bitstream/123456789/4831/1/unit%201.pdf)

Floppy disks and hard disks are commonly used types of magnetic disk. Several other kinds of removable •magneticmediaareinuse,suchastheZipdisk.Allofthesehaveamuchhighercapacitythanfloppydisks,buteach type of media requires its own drive.

Hard DisksThese consist of 1 or more metal platters which are sealed inside a case. The metal is one which is magnetic. •The hard disk is usually installed inside the computer's case, though there are removable and cartridge types, •also. Technically, a • hard drive controls the motion of the hard disks containing the data. Though, most people use ‘hard disk’ and ‘hard drive’ interchangeably.

Floppy DisksAfloppydiskismadeofaflexiblethinsheetofplasticmaterialwithamagneticcoatingandgroovesarranged•in concentric circles with tracks. Disk is removable from the reading device attached to the computer and therefore provides unlimited storage •capacity. Thefloppydisksareavailableintwosizes-5.25inchesand3.5incheswithcapacityrangingfrom360KBto•1.44MBperdisk.However,useoffloppydiskshascompletelystopped,duetothevolatilityandavailabilityof other improved mediums.

3.6.3 Magnetic Tapes

Magnetic tapes are mounted on reels or a cartridge or a cassette of tape to store large volumes or backup data. •These are cheaper and since are removable from the drive, they provide unlimited storage capacity. Information •retrieval from tapes is sequential and not random. These are not suitable for on-line retrieval of data, since sequential searching will take long time. These are •convenient for archival storage, or for backup. The tapes are one of the earliest storage devices having low cost, low speed, portability.•

3.6.4 Optical DisksIn optical storage devices, the information is written using laser beam on a plastic coated disk which can store digital data as tiny pits etched in the surface.

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Characteristics of optical disksThey are formed of layers•Data is in a spiral groove, starting from the centre of disk•Data is in digital format (1s and 0s)•1sand0sareformedbyhowthediskabsorbsorreflectslightfromthetinylaserbeam.•

Working of optical disksAn optical disk is made up of polycarbonate (a plastic). The data is stored on a layer inside the polycarbonate. •Ametallayerreflectsthelaserlightbacktoasensor.To read the data on a disk, laser light shines through the polycarbonate and hits the data layer. How the laser •lightisreflectedorabsorbedisreadasa1or0bythecomputer.In a Compact Disk (CD), the data layer is near the top of the disk, the label side.•In a DVD, the data layer is in the middle of the disk. A DVD can actually have data in two layers. It can access •the data from one side or from both sides. This is how a double-sided, double-layered DVD can hold 4 times the data that a single-sided, single-layered •DVD can.

Types of optical disksFollowing are the types of optical disksRead Only

The most common type of optical disk is the CD-ROM, which stands for Compact Disk Read Only Memory. •It looks just like an audio CD but the recording format is quite different. CD-ROM disks are used for storing computer software.DVD stands for Digital Video Device or Digital Versatile Device: DVDs are used for recording movies and •store large amounts of data.Write Once Read Many: The CDs and DVDs that are commercially produced are of the Write Once Read Many •(WORM) variety. They can't be changed once they are created. That is, they allow writing only once, while data may be read many times.The data layer is physically moulded into the polycarbonate. Pits (depressions) and lands (surfaces) form the •digitaldata.Ametalcoating(usuallyaluminium)reflectsthelaserlightbacktothesensor.Oxygencanseepinto the disk, especially in high temperatures and high humidity. This corrodes the aluminium, making it too dulltoreflectthelasercorrectly.CD-ROM and DVD-ROM disks are readable for many years, if stored in good condition.•

Write OnceThe optical disks that you can record on your own computer are CD-R, DVD-R, and DVD+R disks, and called •as writable or recordable disks. Here, the metal and data layers are separate and metal layer can be of gold, silver, or a silver alloy.•Gold layers are best because gold does not corrode. Naturally, the best is more expensive. Sulphur dioxide in •air can seep in and corrode silver over time.Thedatalayerisanorganicdyethatthewritinglaserchanges.Oncethelasermodifiesthedye,itcannotbe•changed again. Ultraviolet light and heat can degrade the organic dye.Awritablediskisusefulasabackupmediumwhenlong-termstorageofdataisrequired.Itislessefficientfor•data that changes often, since a new recording is required each time the changed data is saved.


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RewriteAn option for backup storage of changing data is • rewritable disks, i.e. CD-RW, DVD-RW, DVD+RW, DVD+RAM. Thedatalayerforthesedisksusesaphase-changingmetalalloyfilm.Thisfilmcanbemeltedbythelaser'sheat•to level out the marks made by earlier data and then again the new data can be recorded with laser. We can erase and write on these disks as many as 1000 times, for CD-RW, and even 100,000 times for the •DVD-RW types.

Advantages of optical disksPhysical:Anopticaldiskismuchsturdierthantapeorafloppydisk.Itisphysicallyhardertobreakormeltor•warp.Delicacy: It is not sensitive to being touched, though it can get too dirty or scratched to be read, but it can be •cleaned. Magnetic:Itisentirelyunaffectedbymagneticfields.•Capacity: Optical disks hold a lot of data, especial the double-sided DVDs. •For software providers, an optical disk is a great way to store the software and data that they want to distribute •or sell.

Disadvantages of optical disksCost•

The cost of a CD-RW has dropped drastically in short period of time. �The cost of disks can add up, too. Recordable disks (one time only) are also getting cheaper. But we have �to be careful about the capacity and maximum recording speed. For commercial use, the read/write drives are quite cost effective. For personal use, they are available and �are cheap enough to use for data storage for everyone.

Duplication•ItisnotquiteaseasyorasfasttocopyanopticaldiskasitistocopyfilestoaUSBflashdrive.Youneed �the software and hardware for writing disks

3.6.5 Flash Memory

Several different brands of removable storage cards, also called as memory cards, are available in the market. •These are solid state devices that read and write data electrically and not magnetically.Deviceslikedigitalcameras,mobilephonesandthelike.mayusecompactflash,smartmedia,memorystick•oranotherflashmemorycard.LaptopsusePCMCIAcards,whichareatypeofflashmemory.Theyareassolidasharddisks.•

3.6.6 USB Drives

Itisalsoknownasflashdrive,jumpdrive,flashpen,keydriveetc.•They can be plugged in to a USB port of computer, without any requirement of drivers.•The storage capacities vary from 8MB to 128GB or more.•

3.6.7 Removable Hard DrivesVarious types of special drives that compress data are available. Since they provide high storage capacity, they can be used for back up as well.

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3.6.8 Smart Cards

A smart card, chip card, or integrated circuit card (ICC) is any pocket-sized card with embedded integrated •circuits. There are two broad categories of ICCs. Memory cards containing only non-volatile memory storage components, •and perhaps dedicated security logic. Microprocessor cards containing volatile memory and microprocessor components. The card is made of plastic. The most common smart card applications are: credit cards, electronic cash, computer •security systems and so on.

3.6.9 Optical CardsThe material is comprised of several layers that react when a laser light is directed at them. The laser burns a tiny hole (2.25 microns in diameter) in the material which can then be sensed by a low power laser during the read cycle.

The presence or absence of the burn spot indicates a 1 or 0. Because the material is actually burned during the •write cycle, the media is a ‘Write Once Read Many’ type and the data is non volatile (not lost when power is removed).Optical cards hold on the order of 1,000x the amount of information as the typical smart card and the data, once •written, is permanent and cannot be erased or altered in any way. Optical cards, unlike smart cards, are also impervioustoelectricandmagneticfieldsandalsotostaticelectricity.

Thus, we now have a complete picture of what the computer consists of and how all the components work together as a process. The idea of how data is received, and how it is processed to give the desired outputs in a required format should be clear.


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SummaryThe core components of a computer are input devices, processor, backing storage devices and output devices.•Data to be processed by computer needs to be converted in a machine readable form which can be done using •various input devices listed.Input can be provided by using any of the options like keyboard, pointing devices, pen input devices, video and •audio input devices or graphical capture.This data is then processed at the CPU which comprises of the Arithmetic Logic Unit, Control Unit and the •Primary Memory, i.e. RAM, ROM and cache.The processed data can be obtained by various output devices. Options for output are visual output devices like •themonitor,audiooutputdevices,hardcopiesthroughprintersandcomputeroutputmicrofilmsThe processed data can also be stored in various secondary storage devices. These storage devices are magnetic •disks,magnetictapes,opticaldisks,flashmemory,USBdrives,smartcards,etc.Storage is useful for further reference and back up.•

ReferencesShelly, B. G. & Vermaat, E. M., 2009. • Discovering Computers: Living in a Digital World : Fundamentals, 6th ed. Cengage Learning.Shim, K. J., 2002. • Information Systems and Technology for the Noninformation Systems Executive: An Integrated Resource Management Guide for the 21st Century, CRC Press.Information Processing 10, 20, 30 Curriculum Guidelines• [Pdf] Available at: <http://www.edcentre.ca/resources/info10/currmain.pdf> [Accessed 28 May 2013].Computer Fundamentals and Troubleshooting• , [Pdf] Available at: <http://infosecawareness.in/downloads/handbooks/computer-fundamentals-and-troubleshooting.pdf> [Accessed 28 May 2013].Prof. Kumar, A., 208. • Lecture -1 Introduction to Computer Architecture [Video online] Available at: <http://www.youtube.com/watch?v=4TzMyXmzL8M> [Accessed 28 May 2013].Janossy, J., • Computer components [Video online] Available at: <http://www.youtube.com/watch?v=kZH3H7XIUuc> [Accessed 28 May 2013].

Recommended ReadingNorton, P., 2002. • Introduction To Computers (Sie), Tata McGraw-Hill Education.Shelly, B. G. & Vermaat, E. M., 2008. • Discovering Computers 2009, Cengage Learning.Shelly, B. G. & Vermaat, E. M., 2011. • Discovering Computers, Brief: Your Interactive Guide to the Digital World, Cengage Learning

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Self AssessmentThe layout of keys is called 1. QWERTY because

QWERTYiseasytotypea. Q-W-E-R-T-Yistheorderinwhichthelettersoccuronthetoprowofthekeyboard.b. It is the name of the keyboardc. It is the basic design of keyboardd.

Immediate access storage is also known as ____________2. primary memorya. secondary memoryb. magnetic diskc. optical diskd.

Which is not a part of graphical capture type of input?3. Barcodea. Smart cardb. Digitizing tabletc. Optical character readersd.

Track balls, joysticks and track pads are all types of ____________ devices.4. pen a. converting b. signal c. pointingd.

Arithmetic logic unit does not constitute of ____________5. data registersa. decodersb. computational circuitsc. accumulatord.

Which of the following is not a type of RAM?6. DRAMa. SRAMb. DDRAMc. SDRAMd.

____________is a dedicated bank of high-speed RAM chips used to cache data from primary memory.7. RAMa. ROMb. Flash memoryc. Memory cached.


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Cathode ray tube display is also known as ____________.8. monitora. logical gateb. computational circuitc. action outputd.

Which of the following is a volatile memory?9. Floppy diska. Optical diskb. Cache memoryc. Flash memoryd.

Which type of storage device uses electricity to write data?10. Hard diska. Flash memoryb. Floppy diskc. Magnetic tapesd.

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Chapter IV

Hardware and Software

Aim


explain the types of hardware and software•

elucidate the concept of programmin language•

explicate systems software•

Objectives


determine the role of motherboard as an important hardware component•

explain the concept of system software and some important types•

explicate application software and its types•

Learning outcome

After end of this chapter, the students should be able to:

undertsand the concept of BIOS •

describe the functions of operating system•

identify the types of operating system•


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4.1 Introduction All physical contents of computer are hardware. This form is given to all electrical and mechanical devices attached to the computer for the purpose of input, process, and storage and output operations. Primary hardware is the CPU and its other units i.e. circuits and IC's. Secondary harware is the memory or storage area of computer.

Software is a general term used for computer Programs. A computer program is a planned, step by step set of instructions that directs the computer what to do and how to do. It turns the data into information - that makes a computer useful.

4.2 HardwareThe electrical, electronic, mechanical, and magnetic components that make up the computer system are together termed as ‘hardware.’ These include components that are responsible for user input, display, and mathematical processing. The CPU, disk drives, internal chips and wiring, modem, peripheral devices like the monitor, keyboard, mouse, printer, speakers and so forth are together termed as computer hardware. Most of the components of hardware have been described and discussed in chapter 2. But an important component to be described here is the ‘Motherboard.’

4.2.1 MotherboardA motherboard is the central Printed Circuit Board (PCB) in many modern computers and holds many crucial components of the system, while providing connectors for other peripherals. The motherboard is sometimes alternatively known as the main board or system board. It is the main component inside the case, consisting of large rectangular board with integrated circuitry that connects the rest of the parts of the computer including the CPU, the RAM, the disk drives (CD, DVD, hard disk, or any others) as well as any peripherals connected via the ports or the expansion slots.

Components directly attached to the motherboard include:The Central Processing Unit (CPU)•The chip set, mediating communication between the CPU and the other components of the system, including •main memoryRAM (Random Access Memory) •TheBasicInputOutputSystem(BIOS),includingbootfirmwareandpowermanagement.ThetasksofBIOS•are handled by operating system drivers.Internal Buses which connect the CPU to various internal components and to expansion cards for graphics and •sound. External Bus Controllers that support ports for external peripherals. These ports may be controlled directly by •the south bridge I/O controller or based on expansion cards attached to the motherboard through the PCI bus.

4.3 SoftwareComputer software, or just software, is the collection of computer programs and related data that instructs a computer to perform desired task or action. We can also say software refers to one or more computer programs and data held inthestorageofthecomputerforsomespecificpurposes.Thetermwascoinedtocontrasttotheoldtermhardware(meaning physical devices). In contrast to hardware, software is intangible, meaning it "cannot be touched."

There are two broad categories of software;Systems software•Application software.•

The process of software development is called programming. Knowledge of programming languages is must to developvariousprograms.Wewillfirsthaveabriefoverviewaboutprogramminglanguagesandthenonthetypesof software.

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4.4 Programming LanguagesProgramming languages are developed with the primary objective of facilitating a large number of people to use computers without the need to know in detail the internal structure of the computer. Languages are also designed to be machine independent. Ideally, one should be able to execute a program on any computer regardless of its manufacturer or model. We can choose any language for writing a program according to the need. But a computer executes programs only after they are represented internally in binary form (sequences of 1s and 0's). Programs written in any other language must be translated to the binary representation of the instructions before they can be executed by the computer.

Important categories or generations of programming languages are described below.

4.4.1 Machine Language

This is a sequence of instructions written in the form of binary numbers consisting of 1's. 0's to which the •computer responds directly. The machine language was initially referred to as code, although now the term code is used more broadly to refer to any program text.Aninstructionpreparedinanymachinelanguagewillhaveatleasttwoparts.ThefirstpartistheCommandor•Operation, which instructs the computer about the function to be performed. All computers have an operation code for each of its functions. ThesecondpartoftheinstructionistheOperandorittellsthecomputerwheretofindorstorethedatathathas•to be manipulated. Justashardwareisclassifiedintogenerationsbasedontechnology,computerlanguagesalsohaveageneration•classificationbasedonthelevelofinteractionwiththemachine.Machinelanguageisconsideredtobethefirstgeneration language.

4.4.2 Assembly Language

When symbols (letters, digits or special characters) are used for the operation part, the address part and other •parts of the instruction code, then such representation is called as an assembly language program. This is considered to be the second generation language. Machine and assembly languages are referred to as •low level languages since the coding for a problem is at the individual instruction level.

4.4.3 High Level Language

High level languages are also called procedural languages. Programming languages such as C, COBOL, •FORTRAN and BASIC are high level languages. As the time and cost for creating machine and assembly languages are high, the high level languages were developed. A program written in a high level language should be translated into a machine compatible form and this is •done by software (language translator) called compiler. A compiler takes a high-level-language program and translates it into an executable machine-language program. There is another kind of software called interpreter which also does the translation.

4.4.4 Fourth Generation Language

FourthGenerationLanguage, referred toas4GL, isahigh level language that requiressignificantly fewer•instructions than a third generation language does to accomplish a particular task. Thus, the programmer should be able to write a program faster in 4GL than in the third generation language. Most 4GLs are non-procedural, i.e. the programmer does not have to give the details of procedure in a program, •but instead specify what is desired.


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4.4.5 Natural Language

Programming languages that use human language to give people more natural interaction with computers are •natural languages. Natural languages allow questions or commands to be framed in a more conversational way. NaturallanguagesarethepartofthefieldofstudyknownasArtificialIntelligence.• Artificialintelligence is a group of related technologies that attempt to develop machines capable of emulating human-like qualities such as learning, reasoning, communicating, seeing, and hearing.

Using any of the suitable programming language, one can write a software program. As described earlier, there are two types of software, which are discussed underneath;

4.5 Systems SoftwareSystem software is computer software designed to operate the computer hardware and to provide and maintain a platform for running application software.

The most basic types of system software are:ThecomputerBIOSanddevicefirmware,whichprovidebasicfunctionalitytooperateandcontrolthehardware•connected to or built into the computer.The operating system (prominent examples being Microsoft Windows, Mac OS X and Linux), which allows •the parts of a computer to work together by performing tasks like transferring data between memory and disks or rendering output onto a display device. It also provides a platform to run high-level system software and application software.Utilitysoftware,whichhelpstoanalyze,configure,optimiseandmaintainthecomputer.•

4.5.1 BIOS

The • BIOS (Basic Input Output System) is the most fundamental software of a computer system. It is the firmware that ‘boots’ your computer, i.e. it starts computer when it is switched on. (This feature is the basis of the BIOS being called a ‘bootstrap program,’ particularly in older computer terminology.) Itchecksyoursystemhardware,loadstheoperatingsystemandfilessystemfromsecondarystorageintoRAM,•executes the operating system and then turns control of the system over to the operating system.TheBIOSalsoassiststheoperatingsystembygoverningtheflowofdatatoandfromperipheraldevices,thus•acting as an interface between input/output devices and the operating system.The BIOS typically is provided on • EEPROM (Electrically Erasable Programmable Read Only Memory). This makes it possible to upgrade system BIOS by ‘flashingyourBIOS’, i.e. writing a new program to the firmware.

4.5.2 Operating System (OS)An operating system is an essential component of a computer system and its primary objective is to make computer systemconvenienttouseandutilisecomputerhardwareinanefficientmanner. AnOSisalargecollectionofsoftware,whichmanagesresourcesofthecomputersystem,suchasmemory,processor,filesystemandinput/outputdevices. It keeps track of the status of each resource and decides who will have a control over computer resources, for how long and when.

Functions of operating systemAllocatingsystemresources:Theoperatingsystemdirectsthetrafficinsidethecomputer,decidingwhatresources•will be used and for how long.Time: Time in the CPU is divided into time slices which are measured in milliseconds. Each task that CPU does •isassignedacertainnumberoftimeslices.Whentimeexpires,anothertaskgetsaturnandthefirsttaskmustwait until it has another turn. Since time slices are so small, you usually can't tell that any sharing is going on. Tasks can be assigned priorities so that high priority (foreground) tasks get more time slices than low priority (background) tasks.

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Memory: Memory must be managed also by the operating system. All those rotating turns of CPU use leave •datawaitingaroundinbuffers.Caremustbetakennottolosedata.Onewaytohelpoutthetrafficjamistousevirtual memory. This includes disk space as part of main memory. While it is slower to put data on a hard disk, it increases the amount of data that can be held in memory at one time. When the memory chips get full, some ofthedataispagedouttotheharddisk.Thisiscalledswapping.Windowsusesaswapfileforthispurpose.Input and output: Flow control is also part of the operating system's responsibilities. The operating system •must manage all requests to read data from disks or tape and all writes to these and to printers. To speed up the outputtoprinters,mostoperatingsystemsnowallowforprintspooling,wherethedatatobeprintedisfirstputinafile.Thisfreesuptheprocessorforotherworkinbetweenthetimeswhendataisgoingtotheprinter.Aprintercanhandlelimitedatatime.Withoutprintspooling,onehastowaitforaprintjobtofinishbeforedoing anything else. With it, one can request several print jobs and go on working. The print spool will hold all the orders and process them in turn.Monitoring system activities: Following are the activities monitored by the OS:•

System performance :A user or administrator can check to see whether the computer or network is getting �overloaded. Changes could be made to the way tasks are allocated. System performance would include response time and CPU utilisation.System security: Some system security is part of the operating system, though additional software can add �more security functions. For multiple users who are not all allowed access to everything, there must be a logon or login procedure where the user supplies a user name or ID and a password. An administrator must set up the permissions list of who can have access to what programs and data.

Fileanddiskmanagement:Keepingtrackofwhatfilesarewhereisamajorjob.Anoperatingsystemcomes•withbasicfilemanagementcommands,where,auserneedstobeabletocreatedirectoriesforstoringfiles.Auserneedstocopy,move,delete,andrenamefiles.Thisisthecategoryofoperatingsystemfunctionsthattheuser actually sees the most. A more technical task is that of disk management. Under some operating systems, hard disk can be divided up or partitioned into several virtual disks. The operating system treats each virtual disk as a physically separate disk. Managing several physical and/or virtual disks can get pretty complex, especially if some of the disks are set up with different operating systems.

Types of operating system Batch operating system: It requires grouping of similar jobs consisting programs, data and system commands. •The suitability of this type of processing is in programs with large computation time with no need of user interaction or involvement. Some examples of such programs include payroll, forecasting, statistical analysis, andlargescientificnumbercrunchingprograms.Usersarenotrequiredtowaitwhilethejobisbeingprocessed.They can submit their programs to system and collect the results later.Multiprogramming operating system: Multiprogramming operating systems, compared to batch operating •systems,arefairlysophisticated.Theyhaveasignificantpotentialforimprovingsystemthroughputandresourceutilisation with very minor differences. Different forms of multiprogramming operating system are multitasking, multiprocessor and multi-user operating systems.Network operating system: A network operating system is a collection of software and associated protocols that •allow a set of autonomous computers, which are interconnected by a computer network, to be used together in a convenient and cost-effective manner. In a network operating system, the users are aware of existence of multiplecomputersandcanlogintoremotemachinesandcopyfilesfromonemachinetotheother.Distributed operating system: A distributed operating system is one that looks like an ordinary centralised •operating system but runs on multiple independent CPUs. The key concept here is transparency. In other words, the use of multiple processors should be invisible to the user. Another way of expressing the same idea is to say that user views the system as virtual uni processor but not as a collection of distinct machines. In a true distributedsystem,usersarenotawareofwheretheirprogramsarebeingrunorwheretheirfilesareresiding;theyareallhandledautomaticallyandefficientlybytheoperatingsystem.


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4.5.3 Utility SoftwareUtility software is a kind of system software designed to help analyse, configure, optimise andmaintain thecomputer. A single piece of utility software is usually called a utility. Utility software usually focuses on how the computer infrastructure, including the computer hardware, operating system, and application software and data storage operates. Due to this focus, utilities are often rather technical and targeted at people with an advanced level of computer knowledge.

4.6 Application SoftwareApplicationsoftwareiswrittentoenablethecomputertosolveaspecificdataprocessingtask.Anumberofpowerfulapplicationsoftwarepackages,whichdoesnotrequiresignificantprogrammingknowledge,havebeendeveloped.These are easy to use and learn, as compared to the programming languages. Although such packages can perform many general and special functions, there are applications where these are not found to be adequate. In such cases, application program is written to meet the exact requirements. A user application program may be written using one of these packages or a programming language.

The most important categories of software packages available are: Data Base Management Software •Spreadsheet Software •Word Processing, Desktop Publishing (DTP), Presentation Software and Graphics Software •

Data Communication Software �Statistical and Operational Research Software. �

We will have a brief overview of some of the application soft wares.

Word ProcessingWord processing is the most used computer application, which has largely replaced the typewriter. It facilitates •revision and correction of documents before they are printed. An existing document can be used as a template, or pattern, for a new one. So the user doesn't have to recreate •standard documents from scratch each time. This is a major time-saver and helps keep things consistent. MicrosoftWord,WordPerfect,LotusWordPro,andOpenOfficeWriteraresomeexamplesofwordprocessing•programs.

Purpose - to produce documents �Main advantage �

easy to edit documents i. can reuse existing documents as a template.ii.

Spread sheetsAspreadsheetistheapplicationofchoiceformostdocumentsthatorganisenumberslikebudgets,financial•statements, grade sheets, and sales records. A spreadsheet can perform simple or complex calculations on the numbers entered in rows and columns. Examples •ofspreadsheetprogramsareMSExcel,Lotus1-2-3,QuattroPro,andOpenOfficeCalc.

Purpose - organising numbers �Main advantage �

can calculate using formulasiii. auto-update of related numbers when data changesiv. can display data in graphs and charts.v.

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Database Management SoftwareA database is a collection of data that is to be managed, rearranged, and to be added to later. With a database •one can sort the data by name or city or postal code or by any individual item of information recorded. One can create forms to enter or update or just display the data or create reports that show just the data of interest, •like members who owe dues and so on.Both spreadsheets and databases can be used to handle much the same information, but each is optimised to handle •adifferenttypemostefficiently.Thelargerthenumberofrecords,themoreimportantthedifferencesare.ExamplesofdatabasesareMSAccess,dBase,FoxPro,Paradox,Approach,Oracle,OpenOfficeBase.•

Purpose - managing data �Major Advantages �

can change the way data is sorted and displayed.vi.

Graphics SoftwareGraphicsprogramsdealwithpictures,staticormoving,flator3D.Thereareanamazingnumberofdifferent•formats for images in the world and no one program can handle them all.Adobe Photoshop is the most widely used graphics program for professionals. Paint Shop Pro is popular because •it offers most of Photoshop's features at a lower cost and with a friendlier interface. There are many other programs, of which, some specialise in handling photographs or animations or creating logos.

Purpose - to create and edit images �Major Advantages �

important tool for professionals in photo or image processingvii. easily creates illustrations, logos.viii.


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SummaryA computer system is a combination of hardware and software.•Computer hardware is the physical part of a computer.•These include components that are responsible for user input, display, and mathematical processing. The CPU, •motherboard, disk drives, internal chips and wiring, modem, peripheral devices like the monitor, keyboard, mouse, printer, speakers and so on are together termed as computer hardware.Computer software is the intangible part unlike the hardware.•Softwaresareclassifiedassystemsandapplicationsoftware.•Both the systems software and the application software are responsible for roles as their names suggests. Systems •software operates the hardware and maintains a platform for running application soft wares.As people need language to write, computer also requires languages to write software programs (both system •software programs and application software programs.) They are known as programming languages.Programming languages are categorised as machine language, assembly language, high level language, and •natural language. Appropriate language is chosen to write programs for systems or application software.

ReferencesBose, K. S., 1996. Hardware And Software Of Personal Computers, New Age International.•Gookin, G., 2011. PCs For Dummies, John Wiley & Sons.•Introduction To Computers: Hardware and Software [Pdf] Available at: <http://pages.cpsc.ucalgary.•ca/~tamj/2005/231W/notes/acrobat/computers_economy.pdf> [Accessed 28 May 2013].BASIC CONCEPTS IN COMPUTER HARDWARE AND BASIC CONCEPTS IN COMPUTER HARDWARE •AND SOFTWARE [Pdf] Available at: <http://wikieducator.org/images/1/11/Basic_Concepts_in_Computer_Hardware_and_Software.pdf> [Accessed 28 May 2013].Intro to Computer Hardware Chapter 1.wmv [Video online] Available at: <http://www.youtube.com/•watch?v=ZOKsmiLcSlo> [Accessed 28 May 2013].Lecture - 3 Introduction To System : Hardware [Video online] Available at: <http://www.youtube.com/•watch?v=FOyuMclwymw> [Accessed 28 May 2013].

Recommended ReadingSchneidewind, F. N., 2012. • Computer, Network, Software, and Hardware Engineering with Applications, John Wiley & Sons.Sichel, E. D., 1997. • The computer revolution: an economic perspective, Brookings Institution Press.Preez, D. A., Dyk, V. V. & Cook, A., 2008. • FCS Computer Hardware & Software L3, Pearson South Africa

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Self AssessmentThe electrical, electronic, mechanical and ____________components that make up the computer system are 1. together termed as ‘hardware’.

maintenancea. magneticb. automaticc. logicald.

Which component of the motherboard mediates communication between the CPU and the other components 2. of the system, including main memory?

Chip seta. RAMb. Biosc. Bus controllerd.

Functions of an operating system are; state which one of the following is false?3. Allocating resourcesa. Monitoring system activitiesb. Creating resourcesc. File and disk managementd.

Multitasking, multiprocessor and multi-user operating systems are sub types of which operating system?4. Network operating systema. Distributed systemb. Batch operating systemc. Multi programming operation systemd.

Data is paged out to the hard disk in case memory chips get full, this is known as ____________ 5. mappinga. swappingb. flaggingc. flappingd.

Operation and operand are parts of which category of programming language?6. Machine languagea. COBOLb. Assembly languagec. Natural languaged.

Identifythesystemsoftwaredesignedtohelpanalyze,configure,optimiseandmaintainthecomputer;7. Windowsa. DOSb. Operating systemc. Utility softwared.


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Time in the CPU is divided into ____________.8. slicesa. sectionsb. factorsc. quartersd.

Which of the following is a non-procedural language?9. Natural languagea. Fourth generation languageb. FORTRANc. C+d.

____________are easy to learn and use as compared to the programming languages.10. System soft waresa. Machine languageb. Application soft waresc. Operation soft waresd.

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Chapter V

Communication and Networks

Aim


explain the communications and network between computers•

elucidate types of communication channel•

explicate the standard networking protocols•

Objectives


explain the role of communication channels in networks•

elucidateclient-to-peerandpeer-to-peernetworkconfiguration•

enlist the types of topology for networks•

Learning outcome


identify and list network communication channels•

understand wired and wireless communication channels•

describe types of topologies and types of networks•


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5.1 IntroductionA standalone computer in today’s context is not very useful, but coupled with communication technology; it opens up an enormous repository of information to its users. The concept of data communication evolved from sharing the computation power of a computer along with various resources available in a computer environment such as printers, hard disk and so on.

With increasing demand for exchange of information across the globe, the need for data communication has increased in many folds. Due to physical constraints involved in connecting two remote points, physical data communication has emerged as an instant solution.

5.2 Computer NetworksIn human life, people connect and relate to each other for various reasons like friendship, common goals, and common work area. Whatever the reason may be, these connections form networks of people. Similarly, for computers, although a standalone computer is of great help and assistance, when more than one computer is involved as a part ofnetwork,theirbeneficialvalueincreasesenormously.Computersmaybenetworked(physically),throughwiresorconnectedwithoutwires.Wewillhaveadetailedaccountofdefinitions,andconceptsrelatedtocommunicationand computer networks in this chapter.

Computernetworksmaybedefinedas,“acollectionofcomputersanddevicesinterconnectedbycommunicationchannels that facilitate communication among users and allows users to share resources.”

5.3 Goals of NetworksNetworks are set up to satisfy certain basic goals. Some of the goals that a network should achieve are:

Cost reduction by sharing hardware and software resources•Provide high reliability by having multiple sources of supply•Provideanefficientmeansoftransportforlargevolumesofdataamongvariouslocations•Provide inter-process communication among users and processors•Reduction in delay driving data transport•Increase productivity by making it easier to share data amongst users•Repairs, upgrades, expansions, and changes to the network should be performed with minimal impact on the •majority of network usersStandards and protocols should be supported to allow many types of equipment from different vendors to share •the network (inter operability)Provide centralised/distributed management and allocation of network resources like host processors, transmission •facilities and so forth.

5.4 Communication ChannelsTo network computers, a physical or non-physical connection needs to be established. This can be achieved using communication channels.

A communication channel is the path—transmission medium—over which information travels in a communication •system from its source to its destination. Channels are also called links, lines, or media.Communication devices use analog electromagnetic signals representing data to transmit information from •one device to another. Electromagnetic signals can travel through vacuum, air or other transmission media like wire,fibreopticsandsoon.Communication channels which use a physical medium for transmission (twisted pair wire, coaxial cable, and •fibreopticcable)arecalledwiredchannels.Communicationchannelswhichdonotrequireanyphysicalmediumfor transmission (radio, microwave and communication satellite) are called wireless channels. The basis for all communication channels both wired and wireless, are the electromagnetic spectrum. The •spectrum covers frequencies for voice, radio waves, infrared light, visible light, and ultraviolet light and X, gamma and cosmic rays.

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5.4.1 Wired Channels (Twisted-pair Wire, Coaxial Cable and Fibre-optic Cable)These media are also called guided media since they provide a conduit from one device to another, a signal travelling along any of these media is directed and contained by the physical limits of the medium.

Wired communication channels use the following physical media:Twisted-pair wire•Coaxial cable•Fibre-optic cable•

Opticalfibreisaglassorplasticcablethatacceptsandtransportssignalsintheformoflight.Letuslookmoreclosely at each of the medium.

Twisted-pair WireTwisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form •of electrical current. Twisted-pair wire are of two types: Unshielded Twisted Pair (UTP) and Shielded Twisted Pair (STP).

Unshielded Twisted Pair (UTP) is the most common type and also used in telephone lines. A twisted pair �consists of two conductors (copper) each with its own coloured plastic insulation and twisted around each other.Twistedpairconfiguration reduces interference fromelectricalfieldascompared toparallelpairconfiguration.Unshieldedtwistedpairiscurrentlythecablestandardformostnetworks.Itisrelativelyinexpensive, easy to install, very reliable, and easy to maintain and expand. UTP support a maximum data rate of 155 Mbps.Shielded Twisted Pair (STP) wire has a metal foil or braided mesh covering that encases each pair of �insulated conductors. The metal casing prevents the penetration of electromagnetic noise and the quality of transmission improves. In all other respects it resembles UTP.

Coaxial CableCoaxial cable (simply called coax) has a central core conductor of solid or standard wire (usually copper) enclosed •in an insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid or a combination of the two (also usually copper).The outer metallic wrapping serves both as a shield against noise and as the second conductor, which completes •the circuit. This outer conductor is also enclosed in an insulating sheath, and the whole cable is protected by a plastic cover. •Coaxial cable carries signals of higher frequency ranges than twisted-pair wire. Often many coaxial cables are bundled together.As a result of extra insulation, coaxial cable is much better than twisted pair wiring at resisting noise. Also, it •is faster than UTP (supports a maximum data rate of 200 Mbps).

Fibre-optic CableThecableconsistsofacoremadeoffineglassorplasticfibre.Thecoreissurroundedbyarefractivelayer•calledthecladdingthateffectivelytrapsthelightandkeepsitbouncingalongthecentralfibre.Inmostcases,the cladding is covered by a buffer layer that protects it from moisture. The entire cable is encased in an outer jacket. Both core and cladding can be made of glass or plastic but must •be of different densities. In addition, the core must be ultra pure and completely regular to ensure distortion- free signals. Since light has higher frequency on the electromagnetic spectrum than other types of radiation such as radio waves, •asinglefibre-opticchannelcancarrymoreinformationthanmostothermeansofinformationtransmission.Hundredsofstrandsofopticalfibres(eachasthinashumanhair)canbehousedinasinglefibre-opticcable.They•represent the most promising type of transmission medium and their usage is fast increasing with the time.


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Themajoradvantagesoffibre-opticcableare:Noise resistance: since fibre-optic transmission uses light rather than electricity, noise (electromagnetic•interference) is not a factor. Less signal attenuation: s signal can run for miles without requiring regeneration.•Higherbandwidth:afibre-opticcablecansupportmuchhigherbandwidththanbothtwisted-pairandcoaxial•cable. It can support data rates of the order of gigabits per second (Gbps). The data rates are limited not by the medium but by the signal generation and reception technology available.•

Themaindisadvantagesoffibre-opticcableare:high cost•difficultiesintheirinstallation/maintenance•fragility.•

5.4.2 Wireless Channels (Radio Link, Microwave Link, Satellite Communication)

Wireless channels transport electromagnetic waves from one point to another through the atmosphere or space •without using a physical conductor. The section of electromagnetic spectrum designated for wireless channels called radio spectrum ranges from •3GHz to 300 GHz and is divided into eight bands each regulated by government authorities. These bands are rated from very low frequency (VLF) to extremely high frequency (EHF). Radio link, microwave •link and satellite communication utilise frequencies in the radio spectrum for data communication.

Radio LinkRadio link, also called as broadcast radio, deals with transmission of data over long distance. A transmitter is •required to send messages and a receiver to receive them. Depending upon the type of the service, it uses a range of frequencies (3 kHz to 30MHz). In the lower frequencies •of radio spectrum, several broadcast radio bands are reserved for conventional AM/FM radio, broadcast television and private radio services.Radio link can support a bandwidth up to 2 Mbps. It is easy to install and involves low recurring costs.•

Microwave LinkMicrowave link, also called as microwave radio, utilises point to point radio transmissions at the super-high •frequency (SHF) and extremely high frequency (EHF) bands. Microwaves do not follow the curvature of the earth and therefore require line-of-sight transmission and reception equipment. Microwave dishes, which contain transceivers (sending and receiving devices) and antennas are set up on towers •or buildings to establish the link. Microwave stations need to be placed at some distances (a few kilometres) from each other with no obstruction •in between. The size of the dish varies with the distance. A string of microwave relay stations is used with each station receiving incoming messages, boosting the signal •strength, and relaying the signal to the next station.Microwave link supports a bandwidth up to 45Mbps and is widely used in data communication.•

Satellite Communication To overcome line-of-sight constraint of microwave earth stations, communication satellites (microwave ‘sky •stations’) are used. Communication satellites are microwave relay stations in orbit around the earth. Transmitting a signal from a ground station to a satellite is called up linking; the reverse is called down •linking.

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Geosynchronous satellites are most commonly used in data communication. A geosynchronous satellite is placed •in geostationary earth orbit (nearly 36,000 km directly above the equator) where it travels at the same speed as the earth and appears to an observer on the ground to be stationary. Consequently,microwaveearthstationsarealwaysabletobeamsignalstoafixedlocationabove.Theorbiting•satellite has solar powered transceivers to receive the signals, amplify them and re-transmit them to another earth station.Satellite communication provides transmission capabilities to and from any location on earth, no matter how •remote. This advantage makes high quality communication available to less developed regions without requiring huge •investment in ground-based infrastructure. Satellite communication supports high bandwidths capable of carrying large amounts of data and ensures low •error rates.

5.5 Transmission TechnologyAfter connecting computers using some communication channel described above, data needs to be transmitted from one computer to another. Transmission technology is necessarily used to do so. There are two types of transmission technologies:

Broadcast networks•Point-to-point or Switched networks•

5.5.1 Broadcast Networks Broadcast networks have a single communication channel that is shared by all the machines on the network. In this type of network, short messages sent by any machine are received by all the machines on the network. The packet containsanaddressfield,whichspecifiesforwhomthepacketisintended.Allthemachines,uponreceivingapacketcheckfortheaddressfield,ifthepacketisintendedforitself,itprocessesitandifnotthepacketisjustignored.

This mode of operation is known as Broadcasting. Some broadcast networks also support transmission to a subset of machines and this is known as Multicasting. One possible way to achieve multicasting is to reserve one bit to indicate multicasting and the remaining (n-1) address bits contain group number. Each machine can subscribe to anyorallofthegroups.Broadcastnetworksareeasilyconfiguredforgeographicallylocalisednetworks.Broadcastnetworks may be static or dynamic, depending on how the channel is allocated.

The different types of broadcast networks are: Packet Radio Networks•Satellite Networks•Local Area Networks. •

Packet Radio broadcasting differs from satellite network broadcasting in several ways. In particular, stations have limited range introducing the need for radio repeaters, which in turn affects the routing, and acknowledges schemes. Also the propagation delay is much less than for satellite broadcasting.

LAN(LocalAreaNetwork)isacomputernetworkthatspansoverarelativelysmallarea.MostLANsareconfinedto a single building or group of buildings within a campus. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide-area network (WAN). There are many different types of LANs, Ethernets being the most common for PCs. A more detailed description of LAN will be covered later in the chapter.


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5.5.2 Point-to-Point or Switched Networks

Point–to-point or switched, networks are those in which there are many connections between individual pairs •ofmachines.Inthesenetworks,whenapackettravelsfromsourcetodestinationitmayhavetofirstvisitoneor more intermediate machines.Routing algorithms play an important role in point-to-point or switched networks, because often multiple routes of •different lengths are available. An example of switched network is the international dial-up telephone system. In Switched network, the temporary connection is established from one point to another for either the duration •of the session (circuit switching) or for the transmission of one or more packets of data (packet switching).

Two types of point- to-point or switched networks are: Circuit Switched Networks

Circuit Switched networks use a networking technology that provides a temporary, but dedicated connection •between two stations no matter how many switching devices are used in the data transfer route. This was originally developed for the analog based telephone system in order to guarantee steady and consistent •service for two people engaged in a phone conversation. Analog circuit switching has given way to digital circuit switching, and the digital counterpart still maintains •the connection until broken (one side hangs up.) This means, bandwidth is continuously reserved and “silence is transmitted” just the same as digital audio in voice conversation.

Packet Switched Networks Packet Switched Networks use a networking technology that breaks up a message into smaller packets for •transmission and switches them to their destination. Unlike circuit switching, which requires a constant point-to-point circuit to be established, each packet in a packet- •switched network contains a destination address. Thus, all packets in a single message do not have to travel the same path. They can be dynamically routed over the network as lines become available or unavailable. Thedestinationcomputerreassemblesthepacketsbackintotheirpropersequence.Packetswitchingefficiently•handles messages of different lengths and priorities. Higher-level protocols, such as TCP/IP, IPX/SPX and NetBIOS, are also packet based and are designed to ride •over packet-switched topologies. Public packet switching networks may provide value added services, such as protocol conversion and electronic mail.

To understand the transmission technology better, we also need to understand the concept of ‘bandwidth’ and its significanceindatatransmission.

5.5.3 Bandwidth

The bandwidth of a communication channel determines its information-carrying capacity. Bandwidth implies •how much data in form of text, voice, video and so on, can be sent through a communication channel in a given amount of time. Foranalogsignals,bandwidthisexpressedinhertz(Hz)andspecifiestherangeoffrequenciesthatthechannel•is capable of transmitting without interference or signal loss.Here bandwidth indicates the difference between the lowest and highest frequencies transmitted. •For example, a microwave link within the range of 800-900 megahertz has a bandwidth of 100 megahertz. •The wider the bandwidth, the faster is the data transmission. The narrower the bandwidth the greater the loss of transmission power, which is overcome by using relays or repeaters that rebroadcast the original signals. Broadband connections are characterised by very high speed. For digital signals, bandwidth is measured in bits per second (bps). The type of the communication channel •determines the channel’s bandwidth.

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Forexample,fibre-opticcableusedforhighspeedinternetaccesshasmorebandwidththanconventionalcopper-wiretelephone lines. High quality voice, music and video transmissions require high bandwidth of the communication channel. Bandwidth plays a critical role while designing a network.

5.6NetworkConfigurationConfigurationreferstothedesignofcomputerswithinanetworktoobtainmaximumefficiency.Therearetwotypesofnetworkconfiguration:

5.6.1 Client-Server Network

Client-Server architecture is one in which the client (personal computer or workstation) is the requesting machine •and the server is the supplying machine, both of which are connected via a local area network (LAN) or wide area network (WAN).A client/server network is called Centralised or Server based network. The client contains the user interface and •may perform some or all of the application processing. Servers can be high-speed microcomputers, minicomputers or even mainframes. A database server maintains the databases and processes requests from the client to extract data from or update •the database. An application server provides additional business processing for the clients. The term client/server is sometimes used to contrast a peer-to-peer network, in which any client can also act as •a server. In that case, a client/server entails having a dedicated server. However, client/server architecturemeansmore thandedicated servers.Simplydownloadingfiles fromor•sharing programs and databases on a server is not true client/server either. True client/server implies that the application was originally designed to run on a network and that the network infrastructure provides the same quality of service as traditional mini and mainframe information systems.

5.6.2 Peer-to-peer Network

A type of network in which each workstation has equal capabilities and responsibilities is called peer-to-peer •network. Each workstation acts as both a client and a server. There is no central repository for information and there is no central server to maintain. •Data and resources are distributed throughout the network, and each user is responsible for sharing data and •resources connected to their system. This differs from client/server architectures, in which some computers are dedicated to serving the others. Peer-to-peer networks are generally simpler and less expensive, but they usually do not offer the same performance •under heavy loads. A peer-to-peer network is also known as a distributed network.

5.7 Network ModelsIn order to divide the workload and to simplify the system design, most of the networks today are organised as a seriesofstackedlayerswitheachlayerstackedoveranothersystemdesign.Itisfurthermoresimplifiedbecausewith a layered architecture, the design has to only concern about the layer in question and not worry about the architecture in a macro sense.

Networkprotocolsarestandardsthatallowcomputerstocommunicate.Aprotocoldefineshowcomputersidentifyone another on a network, the form that the data should take in transit, and how this information is processed once it reaches itsfinaldestination.Protocols alsodefineprocedures forhandling lost ordamaged transmissionsor"packets.”

5.7.1 OSI Reference Model

TheOpenSystemInterconnection(OSI)modelisasetofprotocolsthatattempttodefineandstandardisethe•data communications process; we can say that it is a concept that describes how data communications should take place.


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The OSI model was set by the International Standards Organisation (ISO) in 1984, and it is now considered the •primary architectural model for inter-computer communications. The Open Systems Interconnection (OSI) reference model describes how information from a software application •in one computer moves through a network medium to a software application in another computer. The OSI reference model is a conceptual model composed of seven layers specifying particular network functions •andintotheselayersarefittedtheprotocolstandardsdevelopedbytheISOandotherstandardbodies.The OSI model divides the tasks involved with moving information between networked computers into seven •smaller, more manageable task groups. A task or group of tasks is then assigned to each of the seven OSI layers.Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently. •This enables the solutions offered by one layer to be updated without affecting the other layers.

Application LayerFacilitates communication betweensoftware application like outlook, IE

Presentation LayerData Representation and Encryption

Session LayerInterhost Communication

Transport LayerEnd-to-End connection and reliability

Network Layerpath determination and logical

addressing

Data Link LayerMAC and LLC - Physical Addressing

Physical LayerMedia, signal and binary

transmmission

DATA

OSI MODEL

SEGMENTS

PACKETS

FRAMES

BITS

LAYERS

Fig. 5.1 OSI reference model(Source: http://www.networkguruz.com/wp-content/uploads/2008/06/osi-reference-model.jpg)

Asseeninthefigure,thereare7layersoftheOSImodel.Theseareasfollows:Application Layer (Layer 7)

Theapplicationlayerisprobablythemosteasilymisunderstoodlayerofthemodel.Thistoplayerdefinesthe•language and syntax that programs use to communicate with other programs. Theapplicationlayerrepresentsthepurposeofcommunicatinginthefirstplace.•For example, a program in a client workstation uses commands to request data from a program in the server. •Commonfunctionsatthislayerareopening,closing,readingandwritingfiles,transferringfilesande-mailmessages, executing remote jobs and obtaining directory information about network resources and so on.

Presentation Layer (Layer 6) The presentation layer performs code conversion and data reformatting (syntax translation). As a translator of •the network; it makes sure that the data is in the correct form for the receiving application. When data are transmitted between different types of computer systems, the presentation layer negotiates and •manages the way data is represented and encoded.

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For example, it provides a common denominator between ASCII and EBCDIC machines as well as between •differentfloating point and binary formats. Sun’sXDRandOSI’sASN.1 are twoprotocols used for thispurpose. This layer is also used for encryption and decryption and it also provides security features through encryption •and decryption.

Session Layer (Layer 5) The session layer decides when to turn communication on and off between two computers. It provides the •mechanism that controls the data-exchange process and coordinates the interaction (communication) between them in an orderly manner. It sets up and clears communication channels between two communicating components. It determines one-way •or two-way communications and manages the dialogue between both parties.Forexample,itmakessurethatthepreviousrequesthasbeenfulfilledbeforethenextoneissent.Italsomarks•significantpartsofthetransmitteddatawithcheckpointstoallowfastrecoveryintheeventofaconnectionfailure.

Transport layer (Layer 4) The transport layer is responsible for overall end-to-end validity and integrity of the transmission, i.e. it ensures •that data is successfully sent and received between two computers. The lower data link layer (layer 2) is only responsible for delivering packets from one node to another. Thus, if •a packet gets lost in a router somewhere in the enterprise internet, the transport layer will detect that. It ensures thatifa12MBfileissent,thefull12MBisreceived.Ifdataissentincorrectly,thislayerhastheresponsibilityofaskingforretransmissionofthedata.Specifically,•it provides a network-independent, reliable message-independent, reliable message-interchange service to the top three application-oriented layers. This layer acts as an interface between the bottom and top three layers. By providing the session layer (layer •5) with a reliable message transfer service, it hides the detailed operation of the underlying network from the session layer.

Network layer (Layer 3) The network layer establishes the route between the sending and receiving stations. The unit of data at the •networklayeriscalledapacket.Itprovidesnetworkroutingandflowandcongestionfunctionsacrosscomputer-network interface. It makes a decision as to where to route the packet based on information and calculations from other routers, •or according to static entries in the routing table. It examines network addresses in the data instead of physical addresses seen in the Data Link layer. •The network layer establishes, maintains, and terminates logical and/or physical connections. It is responsible •for translating logical addresses, or names, into physical addresses. The main device found at the network layer is a router.

Data Link Layer (Layer 2) The data link layer groups the bits that we see on the Physical layer into Frames. It is primarily responsible for •error-free delivery of data on a hop. The data link layer is split into two sub-layers i.e.,

The Logical Link Control (LLC) �Media Access Control (MAC). �

The data link layer handles the physical transfer, framing (the assembly of data into a single unit or block), •flowcontrolanderror-controlfunctions(andretransmissionintheeventofanerror)overasingletransmissionlink; it is responsible for getting the data packaged and onto the network cable. The data link layer provides the network layer (layer 3) reliable information-transfer capabilities.


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The main network device found at the data link layer is a bridge. This device works at a higher layer than the •repeater and therefore is a more complex device. It has some understanding of the data it receives and can make a decision based on the frames it receives as to •whether it needs to let the information pass, or can remove the information from the network. This means that theamountoftrafficonthemediumcanbereducedandtherefore,theusablebandwidthcanbeincreased.

Physical Layer (Layer 1) Thedataunitsonthislayerarecalledbits.Thislayerdefinesthemechanicalandelectricaldefinitionofthe•network medium (cable) and network hardware. This includes how data is impressed onto the cable and retrieved from it. The physical layer is responsible for passing bits onto and receiving them from the connecting medium. This layer •gives the data-link layer (layer 2) its ability to transport a stream of serial data bits between two communicating systems; it conveys the bits that move along the cable. It is responsible for ensuring that the raw bits get from one place to another, no matter what shape they are in, •and deals with the mechanical and electrical characteristics of the cable.

5.7.2 TCP/IP Protocol

TCP/IP stands for Transmission Control Protocol/Internet Protocol. •It is a protocol suite used by most communications software. TCP/IP is a robust and proven technology that was •firsttestedintheearly1980sonARPANet,theU.S.military’sAdvancedResearchProjectsAgencyNetwork,andtheworld’sfirstpacket-switchednetwork.TCP/IP was designed as an open protocol that would enable all types of computers to transmit data to each other •via a common communications language. TCP/IP is a layered protocol similar to the ones used in all the other major networking architectures, including •IBM’s SNA, Windows' NetBIOS, Apple’s AppleTalk, Novell’s NetWare and Digital's DECnet. There are 4 layers. Layering means that after an application initiates the communications, the message (data) to •be transmitted is passed through a number of stages or layers until it actually moves out onto the wire. The data are packaged with a different header at each layer. At the receiving end, the corresponding programs •at each protocol layer unpack the data, moving it “back up the stack” to the receiving application. TCP/IP is composed of two major parts: TCP (Transmission Control Protocol) at the transport layer and IP •(Internet Protocol) at the network layer. TCP is a connection-oriented protocol that passes its data to IP, which is connectionless one. TCP sets up a •connection at both ends and guarantees reliable delivery of the full message sent. TCP tests for errors and requests retransmission if necessary, because IP does not do that.

5.8 Network TopologiesTopology refers to the shape of a network, or the network’s layout. How different nodes in a network are connected to each other and how they communicate with each other is determined by the network's topology. Topologies are either physical or logical.

Some of the most common network topologies are:Bus topology•Star topology•Ring topology•Tree topology•Mesh topology•

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The parameters that are to be considered while selecting a physical topology are:Ease of installation•Easeofreconfiguration•Ease of troubleshooting.•

Bus TopologyIn Bus topology, all devices are connected to a central cable, called the bus or backbone. The bus topology •connects workstations using a single cable. Each workstation is connected to the next workstation in a point-to-point fashion. All workstations connect to •the same cable.

BackboneCable tap

Drop cable

Terminator

Fig. 5.2 Bus topology(Source: http://www.egyankosh.ac.in/bitstream/123456789/7399/1/Unit%201.pdf)

Advantages of Bus Topology Installation is easy and cheap when compared to other topologies•Connections are simple and this topology is easy to use•Requires less cabling. •

Disadvantages of Bus Topology Used only in comparatively small networks•As all computers share the same bus, the performance of the network deteriorates when the number of computers •is increased beyond a certain limitFaultidentificationisdifficult•A single fault in the cable stops all transmission. •

Star TopologyStar topology uses a central hub through which all components are connected. In a Star topology, the central •hub is the host computer, and there is a terminal at the end of each connection.Nodescommunicateacrossthenetworkbypassingdatathroughthehub.Astarnetworkusesasignificantamount•of cable as each terminal is wired back to the central hub, even if two terminals are side by side but several hundred meters away from the host. The central hub makes all routing decisions, and all other workstations can be simple.


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Fig. 5.3 Star topology(Source: http://www.egyankosh.ac.in/bitstream/123456789/7399/1/Unit%201.pdf)

Advantages of Star Topology Easy to install and wire•No disruptions to the network when connecting or removing devices•Easy to detect faults and to remove parts. •

Disadvantages of Star Topology Requires more cable length than a linear topology•If the hub, switch, or concentrator fails, nodes attached are disabled•More expensive than linear bus topologies because of the cost of the hubs, etc.•

Ring TopologyIn ring topology, all devices are connected to one another in the shape of a closed loop, so that each device is •connected directly to two other devices, one on either side of it.Each terminal is connected to two other terminals (the next and the previous), with the last terminal being •connectedtothefirst.Dataistransmittedaroundtheringinonedirectiononly;eachstationpassingonthedatato the next station till it reaches its destination. Information travels around the ring from one workstation to the next. Each packet of data sent on the ring is •prefixedbytheaddressofthestationtowhichitisbeingsent.Whenapacketofdataarrives,theworkstationchecks to see if the packet address is the same as its own, if it is, it grabs the data in the packet. If the packet does not belong to it, it sends the packet to the next workstation in the ring. The common implementation of this topology is token ring. A break in the ring causes the entire network to •fail. Individual workstations can be isolated from the ring.

Fig. 5.4 Ring topology(Source: http://www.egyankosh.ac.in/bitstream/123456789/7399/1/Unit%201.pdf)

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Advantages of Ring Topology Easy to install and modify the network•Faultisolationissimplified•Unlike bus topology, there is no signal loss in ring topology because the tokens are data packets that are re-•generated at each node.

Disadvantages of Ring Topology Adding or removing computers disrupts the entire network •A break in the ring can stop the transmission in the entire network•Findingfaultisdifficult•Expensive when compared to other topologies. •

Tree TopologyTree topology is a LAN topology in which only one route exists between any two nodes on the network. The •pattern of connection resembles a tree in which all branches spring from one root. Tree topology is a hybrid topology. It is similar to the star topology but the nodes are connected to the secondary •hub,whichinturnisconnectedtothecentralhub.Inthistopology,groupsofstar-configurednetworksareconnected to a linear bus backbone.

Fig. 5.5 Tree topology(Source: http://www.egyankosh.ac.in/bitstream/123456789/7399/1/Unit%201.pdf)

Advantages of Tree TopologyInstallationandconfigurationofnetworkiseasy•Less expensive when compared to mesh topology•Faults in the network can be detected•The addition of the secondary hub allows more devices to be attached to the central hub•Supports multiple cable types like shielded twisted pair cable, unshielded twisted pair cable, ordinary telephone •cable and so forth.

Disadvantages of Tree TopologyFailure in the central hub brings the entire network to a halt•More cabling is required when compared to bus topology because each node is connected to the central hub.•


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Mesh TopologyMesh topologies are used in critical connection of host computers (typically telephone exchanges). Alternate •paths allow each computer to balance the load to other computer systems in the network by using more than one of the connection paths available. A fully connected mesh network therefore has n (n-1)/2 physical channels to link n devices. To accommodate •these, every device on the network must have (n-1) input/output ports.

Fig. 5.6 Mesh topology(Source: http://www.egyankosh.ac.in/bitstream/123456789/7399/1/Unit%201.pdf)

Advantages of Mesh Topology Useofdedicatedlinkseliminatestrafficproblems•Failure in one of the computers does not affect the entire network•Point-to-point link makes fault isolation easy•It is robust•Privacy between computers is maintained as messages travel along dedicated path. •

Disadvantages of Mesh Topology The amount of cabling required is high•A large number of I/O (input/output) ports are required.•

5.9 Types of NetworksForusinganyofthesuitablecommunicationchannels,networkconfiguration,andtopology,therearedifferenttypesof networks which are based on geographical areas of work. Common examples of network are Novell network, ARPANET and internet.

Features of Local Area Network (LAN) are:All connected devices in the network share the transmission media •Each device connected in the network can either operate standalone or in the network•

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Area covered is small•Data transfer rates are high, usually 1Mbps-100Mbps (Million of bits per second)•Each device connected in the network can communicate with any other device in network•Cost of setting up the network is usually low.•

Metropolitan Area Network (MAN): Metropolitan Area Network is a computer network designed for a town or city. In terms of geographic area, MAN’s are larger than LANs, but smaller than wide-area networks (WANs). MAN’s are usually characterised by very high-speedconnectionsusingfibreopticalcableorotherdigitalmedia.

The typical characteristics of a MAN are: ConfinedtoalargerareathanaLANandcanrangefrom10kmtoafew100kminlength•Slower than a LAN but faster than a WAN •Operates at a speed of 1.5 to 150 Mbps•Expensive equipment•Moderate error rates. •

Wide Area Network (WAN)Wide Area Network is a computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs). They can connect networks across cities, states or even countries.

Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites.

The typical characteristics of a WAN are: A WAN can range from 100km to 1000km and the speed between cities can vary form1.5 Mbps to 2.4 Gbps•WAN supports large number of computers and multiple host machines•Various segments of network are interconnected using sophisticated support devices like routers and •gatewaysUsually the speed is much slower than LAN speed•Highest possible error rate compared to LAN & MAN.•

An overview and comparison of different characters of types of networks is given below.

NETWORK SIZE TRANSMISSION MEDIA MAXIMUM DISTANCE

Local Area Network Confinedtobuildingorcampus

Cable is used Covers up to 10 km

Metropolitan Area Network

Networkconfinedtocityor town

Different hardware & transmission media are used

Covers the area of a city or town

Wide Area Network Larger than MAN Telephone lines, radio waves, leased lines or satellites

Covers a number of cities or countries

Table 5.1 Types of networks(Source: http://www.egyankosh.ac.in/bitstream/123456789/7399/1/Unit%201.pdf)

Thus, computers in a networked environment provide numerous advantages when compared to computers in a standaloneenvironment.Theimmensebenefitsthatthecomputernetworksprovideareintheformofexcellentsharingofcomputationalresources,computationalload,andincreasedlevelofreliability,economyandefficientperson-to-person communication.


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SummaryComputer network is a collection of computers and a device interconnected by communication channels that •facilitate communication among users and allows users to share resources.Communication channels which use a physical medium for transmission (twisted pair wire, coaxial cable, and •fibreopticcable)arecalledwiredchannels.Communicationchannelswhichdonotrequireanyphysicalmediumfor transmission (radio, microwave and communication satellite) are called wireless channels. The basis for all communication, a channel both wired and wireless, is the electromagnetic spectrum. The •spectrum covers frequencies for voice, radio waves, infrared light, visible light, and ultraviolet light and X, gamma and cosmic rays.Configurationreferstothedesignofcomputerswithinanetworktoobtainmaximumefficiency.Therearetwo•typesofnetworkconfiguration,client-to-serverandpeer-to-peer.There are two types of transmission technologies, broadcast networks and point-to-point or switched •networksStandards for network communication followed are OSI reference model and TCP/IP protocol•Topology refers to the shape of a network, or the network’s layout. How different nodes in a network are •connected to each other and how they communicate with each other is determined by the network's topology. Topologies are either physical or logical.Some of the most common network topologies are: bus topology, star topology, ring topology, tree topology, •and mesh topology.Types of networks are LAN, MAN, WAN. Common examples of network are Novell network, ARPANET and •internet.Benefits that the computer networks provide are in the form of excellent sharing of computational •resources, computational load, and increased level of reliability, economy and efficient person-to-personcommunication.

ReferencesKesidis, G., 2007. • An Introduction to Communication Network Analysis, John Wiley & Sons.Stallings, W., 2007. • Data And Computer Communications, 8/E, 8th ed. Pearson Education India.Hoang, D. B. & Pye, K. J., • Computer Communication Networks - Lecture Notes [Pdf] Available at: <ftp://cs.istu.ru/public/docs/other/_New/Sciense/books.pdox.net/Lecture@2520Notes/Computer%20Communication%20Networks%20-%20Latrobe.pdf> [Accessed 28 May 2013].Computer networks, data communication and Internet• [Pdf] Available at: <http://www.vub.ac.be/BIBLIO/nieuwenhuysen/courses/chapters/network.pdf> [Accessed 28 May 2013].Protocols and Computer Networks part 1• [Video online] Available at: <http://www.youtube.com/watch?v=Q3SsVO0eSOU> [Accessed 28 May 2013]Prof. Ghosh, S., L• ecture -1 Emergence of Networks & Reference Models [Video online] Available at: <http://www.youtube.com/watch?v=3DZLItfbqtQ&list=PLD6F332057F76C54C> [Accessed 28 May 2013].

Recommended ReadingKasera, S. & Narang, N., 2005. • Communication Networks: Principles and Practice, Tata McGraw-Hill Education.Bagad, V.S. & Dhotre, I. A., 2009. • Computer Communication Networks, Technical Publications.Mir, F. N., 2006.• Computer and Communication Networks, Pearson Education.

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Self AssessmentWhich of the following is not a goal of computer networks?1.

Cost reduction by sharing hardware and software resourcesa. Provide high reliability by having multiple sources of supplyb. Increase productivity by making data un-sharablec. Repairs, upgrades, expansions, and changes to the network should be performed with minimal impact on d. the majority of network users

Noise resistance, higher bandwidth, and less signal attenuation are advantages of using which type of connecting 2. channel?

Shielded twisted pair cablea. Fiber optic cableb. Unshielded twisted pair cablec. Coaxial cabled.

Geosynchronous satellite is placed in geostationary earth orbit where it travels at the ____________as the 3. earth.

same speeda. double speedb. half the speedc. maximum speedd.

When broadcast networks support transmission to a subset of machines, it is known as ____________.4. broadcastinga. transmissionb. networkingc. multicastingd.

Routing algorithms play an important role in which type of network transmission?5. Switched networksa. Packet radio networksb. Satellite networksc. Broadcast networksd.

OSImodelisasetofprotocolsthatattempttodefineand____________-thedatacommunicationsprocess.6. authorisea. standardiseb. speed-upc. eased.

‘Packet’ is the unit of data in which layer of the OSI model?7. Application layera. Transport layerb. Network layerc. Physical layerd.


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TCP/IP is a protocol suite used by most ____________software.8. networka. systemsb. applicationc. communicationsd.

Which are the parameters that are to be considered while selecting a physical topology? (State which is not 9. TRUE)

Ease of installationa. Ease of drawing the networkb. Easeofreconfigurationc. Ease of troubleshootingd.

Computers connected to a wide-area network are often connected through: (State which is not TRUE)10. Connectorsa. Public networks, b. Leased lines c. Satellites d.

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Chapter VI

Operating Systems

Aim


introduce basic organisation of computer systems•

elucidate history of DOS•

explainbatchfilesandbatchsystem•

Objectives


explain spooling•

explicate essential properties of the operating system batch•

defineoperatingsystem,functions,historyandevolution•

Learning outcome


analyse multiprogramming•

identify time sharing system•

understand internal and external commands of DOS•


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6.1 IntroductionAn operating system acts as an intermediary between the user of a computer and computer hardware. The purpose of an operating system is to provide an environment in which a user can execute programs in a convenient and efficientmanner.Anoperatingsystemissoftwarethatmanagesthecomputerhardware.Thehardwaremustprovideappropriate mechanisms to ensure the correct operation of the computer system and to prevent user programs from interfering with the proper operation of the system.

6.2 Operating SystemAn Operating system is a program that controls the execution of application programs and acts as an interface between theuserofacomputerandthecomputerhardware.Amorecommondefinitionisthattheoperatingsystemistheoneprogram running at all times on the computer (usually called the kernel), with all else being applications programs. An Operating system is concerned with the allocation of resources and services, such as memory, processors, devices and information. The Operating System correspondingly includes programs to manage these resources, such as a trafficcontroller,ascheduler,memorymanagementmodule,I/Oprograms,andafilesystem.

6.2.1 Functions of Operating SystemOperating system performs three functions:

Convenience: An OS makes a computer more convenient to use.•Efficiency:AnOSallowsthecomputersystemresourcestobeusedinanefficientmanner.•Ability to Evolve: An OS should be constructed in such a way as to permit the effective development, testing •and introduction of new system functions without at the same time interfering with service.

6.2.2 Operating System as User InterfaceEvery general purpose computer consists of the hardware, operating system, system programs and application programs. The hardware consists of memory, CPU, ALU, I/O devices, peripheral device and storage device. System program consists of compilers, loaders, editors, OS etc. The application program consists of business program, database program. The Figure shows the conceptual view of a computer system.

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user1

user2

user3

compiler assembler text editor databasesystem

system and application programs

operating system

Computer Hardware

usern

Fig. 6.1 Conceptual view of a computer system

Every computer must have an operating system to run other programs. The operating system coordinates the use of the hardware among the various system programs and application program for a various users. It simply provides an environment within which other programs can do useful work.

The operating system is a set of special programs that run on a computer system that allow it to work properly. Itperformsbasictaskssuchasrecognisinginputfromthekeyboard,keepingtrackoffilesanddirectoriesonthedisk, sending output to the display screen and controlling the peripheral devices. OS is designed to serve two basic purposes:

It controls the allocation and use of the computing system‘s resources among the various user and tasks.•Itprovidesaninterfacebetweenthecomputerhardwareandtheprogrammerthatsimplifiesandmakesfeasible•for coding, creation, debugging of application programs.

The operating system must support the following tasks. The tasks are:Providesthefacilitiestocreate,modificationofprogramanddatafilesusingandeditor.•Access to the compiler for translating the user program from high level language to machine language.•Provide a loader program to move the compiled program code to the computer‘s memory for execution.•Provide routines that handle the details of I/O programming.•


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6.3 History of Operating SystemOperating systems have been evolving through the years. Following table shows the history of OS.

Generation Year Electronic devices used Types of OS and devices

First 1945 – 55 Vacuum tubes Plug boards

Second 1955 – 1965 Transistors Batch system

Third 1965 – 1980 Integrated Circuit (IC) Multiprogramming

Fourth Since 1980 Large scale integration PC

Table 6.1 History of OS

6.4 Disk Operating System DiskOperatingSystem (specifically) anddiskoperating system (generically),most often abbreviated asDOS(not to be confused with the DOS family of disk operating systems for the IBM PC compatible platform), refer to operating system software used in most computers that provides the abstraction and management of secondary storagedevicesandtheinformationonthem(e.g.,filesystemsfororganisingfilesofallsorts).Suchsoftwareisreferred to as a disk operating system when the storage devices it manages are made of rotating platters (such as harddisksorfloppydisks).

In the early days of micro computing, memory space was often limited, so the disk operating system was an extension of the operating system. This component was only loaded if it was needed. Otherwise, disk-access would be limited to low-level operations such as reading and writing disks at the sector-level. In some cases, the disk operating system component (or even the operating system) was known as DOS. Sometimes, a disk operating system can refer to the entire operating system if it is loaded off a disk and supports the abstraction and management of disk devices. An example is DOS/360. On the PC compatible platform, an entire family of operating systems was called DOS.

6.4.1 History of DOS In the early days of computers, there were no disk drives; delay lines, punched cards, paper tape, magnetic tape, magnetic drums, were used instead. And in the early days of microcomputers, paper tape or audio cassette tape or nothing were used instead. In the latter case, program and data entry was done at front panel switches directly into memory or through a computer terminal / keyboard, sometimes controlled by a ROM BASIC interpreter; when power was turned off after running the program, the information so entered vanished.

Bothharddisksandfloppydiskdrivesrequiresoftwaretomanagerapidaccesstoblockstorageofsequentialandother data. When microcomputers rarely had expensive disk drives of any kind, the necessity to have software to manage such devices (i.e., the disks) carried much status. To have one or the other was a mark of distinction and prestige, and so was having the Disk sort of an Operating System. As prices for both disk hardware and operating system software decreased, there were many such microcomputer systems.

6.4.2 Components of MS-DOSDOS is an Operating System. It works as an interpreter between user and computer. We give English like commands and it converts it into machine language and after the computer has processed the information, returns the results to you in English. Ms. Dos consist of four essential programs and a set of additional utilities.

MS-DOS consists of four essentials programs and a set of additional utilities. Four main programs are:Boot Record•IO.SYS•MSDOS.SYST•

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COMMAND.COM•Booting: Process that starts up a computer is called booting. It checks for proper functioning of all the peripheral devices attached with the system. It searches for the operating system and, when located, loads it into the main memory.

Cold Booting is done by turning on the computer.•Warm Booting is performed by pressing Ctrl+Alt+Del keys simultaneously.•

There are two name in DOS and is divided into 2 parts.Primary Name•Secondary or extension.•

Primary name is separated from the Secondary name extension with the help of a dot (.) look at the following example.

Example: ENVOICE. TXT

Primary name can be from 1 to 8 characters long and Secondary name contains 3 or less than 3 characters and is optional.TheextensiontellsDOSaboutwhatkindoffileitis.ValidCharactersfornamingafileare:fromAtoZand the digit 0 to 9

C :\> Is known as DOS/command prompt, where we give the commands.

DOS command divided into 2 parts:Internal Commands or Memory-Resident Commands•External Command or Disk-Residence Commands•

6.4.3 Internal CommandThere are also called memory-resident commands. These commands are automatically loaded into the computer’s memoryduringthebootingprocess.TheyactuallyincludedintheCommand.comfile.Sothesecommandsareexecutable immediately after getting the dos prompt. A few internal commands are:

VER•VOL•DATE •TIME •CLS•DIR•MD•CD•PATH•RD•COPYCON•TYPE•COPY•DEL•REN •PROMT•


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A command can be given in Capitals or Small letters also. The internal commands can execute immediately but ExternalCommandsrequirespecialfilesfortheirexecutionwithoutwhichitisnotpossibletoexecutethem.

VER: All O/S has its own edition number or release or version number. The version number indicates which edition of O/S you are working on.Syntax: VER <Enter>Example: C:\> Ver <Enter>Result will be: - Microsoft Windows XP [Version 5.1.2600]

VOL: It is used to display volume label and serial number of the current driveSyntax: Vol [drive:]Example: C:\> VOL

DATE: Used to display the current system date and prompt for entering new date.Syntax: Date <Enter>Example: C:\> date <Enter>

TIME: Displays the current system time and prompt for entering new time.Syntax: Time <Enter>Example: C:\> Time <Enter>

CLS: Clears the cluster screen.Syntax: CLS <Enter>Example: C:\> CLS <Enter>

DIR:Thiscommanddisplaysthelistofdirectoriesandfileswithdetailslikedateofcreationwhetheritisdirectoryorfileetc.Syntax: DIR <Enter>Switches:/p :Toviewonescreenoffilesatatime./w :Displaysonlyfivecolumnoffilenamesanddirectories./b :Displayonlyfileanddirectory./l : Display all the information in lower case letters.

/a : stands for attributes that are given below/-h :Hidden(ornothidden)filess/-s :System(ornotsystems)filesd/-d : Directory (or not Directory) namesr/-r :Readonly(ornotreadonly)files

Example:DIR*.txt :Displayallthefileswithextension.txtDIRD???.* :DisplayallthefilesstartingwithDandhavinglessthanorequaltofourcharactersinthefilenameand any extension.

Here “?” And “*” are called “wild card character”“*” Stand for any number of the character“?” Stands for nay one character

MD OR MKDIR: Used to create a new Directory or nested DirectoriesSyntax:MKDIRORMD[DRIVE:]PATHDIRECTORYNAMEExample: C:\> MD SAMS <Enter>

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CD OR CHDIR: This command allows changing present directory to another directory.Syntax: CD [DRIVE:] PATHExample: C:\> CD SAMS and press <Enter>

PATH:ThiscommanddefinesalistofdirectoriesDOSSearchesforexternalcommandsSyntax: PATH (Display the current Search Path)PATH; : ( Clear the search path so DOS will search for external commands only in the current directory)

RD: To delete the empty directory.Syntax: RD [DRIVE:] PATH

NOTE: The directory must be empty when we use RD.Example: C:\> RD SAMS and press <Enter>Switches /s–Removewithsubdirectoriesandfiles./q–Don’tasktoconfirm.

COPY CON: Weusethiscommandtocreateanewfile.Syntax:COPYCON<FILENAME>Example: C:\> Copy Con sams.txt <Enter>Note: - Typing here and when you are done, press Ctr+Z or F6 key followed by Enter to save the current document.

TYPE:Thiscommandallowsyoutoseethecontentsofanexistingfileonthescreen.SYNTAX:TYPE<filename>Example:C:\>TYPESAMS

COPY:Usingthiscommandyoucanmakeduplicatefilesofanexistingfilefromonelocationtoanotheroronedirectory to another with different name or exiting name.

SYNTAX:COPY<SOURCEFILENAME><TARGETFILENAME>Example:C:\>COPYSAMS.TXTA:\TAJExample:C:\>COPY*.TXT+*.BAKTARGETFILENAMEAndThenPressEnterExample:C:\>COPYSAMS.TXTC:\SAMS_1\FO\RECEPTIONAndThenPressEnter

Youcanalsohavetheoptiontochangethenameoffilesasyoucopyit.Example:C:\>COPYold.TXTC:\dos\new.txtAndThenPressEnter

DEL/ERASE:Thiscommandremovesoneormorefilesfromthediskorcurrentworkingdirectories.SYNTAX:DELfilespec[/p]orERASEfilespec[/p]Example: C:\> DEL C:*.BAK /P And Then Press EnterExample: C:\> DEL abc And Then Press EnterExample: C:\> DEL ????.COM And Then Press EnterSwitches /p–confirmation/q – In quit mode

REN:Usedtochangethenameofthefileordirectory.SYNTAX:REN<filename>Example: REN sams sams1 <Enter>Example: REN *.dat *.mst And Then Press Enter

PROMPT: This command allows you to customise the dos promptSYNTAX:1.PROMPT


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Character Example Description

$Q = Equal Sign

$$ $ Dollar Sign

$t 12:30:06:92 Display current time

$ d tue 09-07-2007 Display current date

$v msdos version 6.2 show dos version number

$g > Greater than sign

$L < Less than sign

Table 6.2 Some Special $ Parameters Are Given Below

Most people like to set their prompt to $p$g which display the current directory followed by > sign.Example: PROMPT $P$G <Enter>

TREE:ItisusedtodisplaydirectorystructureofaspecifieddirectorygraphicallySyntax : TREE [drive:] [path] [/f][/F] :displaysthenamesofthefilesineachdirectory

6.4.4 External CommandsThese are also called Disk-Resident Commands. These commands are meant for special purpose. These are found inseparatefilesonHardDiskorFloppyDisk,Sothattheydon’ttypicallyconsumevaluablememoryspace.Theyare loaded into memory only when called. Some External Commands are:

Xcopy•Move•FC•Doskey•Mem•FILTER•

More �Sort �Find �

Attrib•Deltree•Edit•Tree•

XCOPYThis command is faster than Copy Command and allows you to copy entire directories/disk including all the sub directoriesandfilestodestination.

Syntax :XCOPYSource[Target][/Y][-Y][/P][/E]

SWITCHES:/-Y :Promptsbeforecopyingoverexistingfiles.

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/y :Overwritesexistingfileswithoutprompting./p :Askbeforecopyingeachfile./e : Copying empty directory also./s : Copying subfolders.

EXAMPLE:XCOPYC:\SAMSD:\SAMS/S/E

MOVEThiscommandmovesafileorgroupoffilesfromonedirectorytoanotherandalsoonedisktoanotherdisk.Itcanalso be used to rename directories.

Syntax:Move[PathFileName][Destinationfilenamepath]

Swiches: /-Y :Promptbeforeitoverwriteswhileitcopiesfilethatalreadyexists./Y :Overwritesexistingfileswithoutprompting.

EXAMPLE: move c:\sams\fo.txt to d:EXAMPLE: move c:\sams\fo.txt to d:\ new_sams

FCStandsforFileCompare.Ifyouwishtocomparetwofilesortwosetsoffilesthenyoumayusethiscommand.Thiscommandhasthecapabilitytodifferentiatebetweenthefilesanddisplaythedifference.

Syntax:FC<filesspec1><filesspec2>[/a][/b][/c][l][/n]

Switches/a :Thisswitchdisplaysonlythefirstandlastlineofeachgroup./b :Comparethefilesinlibrarymode(byte-by-byte)/c :Ignorethecaseofletters./l:Comparethefilesintextmode./n : Displays the line number for lines that are different.

EXAMPLE:FCfirst.txtsecond.txt\nandthenPress<enter>

DOSKEYDos can remember only the last command you had entered. But in order to make DOS remember all the commands youenteryouwillhavetoloadaDOSKEYutility.AlsoUsedToCreateMacrosSyntax:DOSKEYandPress<Enter>Display message on the screen.DOSKEYInstalled.

NOTE :To display all commands from the history list one the screen.

Example:DOSKEY/Historyor/h<Enter>.

NowwhenDOSKEYisinmemory,itcanhelpstoreallthecommandswhichyouentersothatanyofthosecommandsneednotbetypedagaintobeexecuted.AndthisallarecalledHISTORYLIST.Nowwhenyouwantthesamecommand to be done you can use right arrow key or ‘F1’ or ‘F3’ Issuing following command.

SecondfeatureofDOSKEYisDoskeyMacro.Usingthismacroyoucancreateowncommandandlatteryoucanrun it on the system prompt.

Forexample“EXAMPLE:-DOSKEYC=CLS”


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Now if you type at the system prompt only C and press enter it will clear the screen.

RecallingCommands:SomekeyisprovidedtorecallrecentcommandsyouhaverunsinceinstallingDOSKEY

Key Strok EffectUp Arrow Display the Preceding Command and further list.Down Arrow Show the next command you executed after the one that’s being displayedPage Up Display the oldest command that is still in DoskeyPage Down Show the most recent command that you executedF7 Display the entire list of command that you executedF9 Selects a commandAlt+F7 Erase the command history list.Alt+F10 Erase all macros in memoryEsc Clear the command line.Ctrl-T Command separator

6.5 UNIXUNIX is one of the very oldest operating systems in the computer world, and is still widely used today. However, it is not a very conspicuous operating system. Somewhat arcane in its operation and interface, it is ideally suited for the needs of large enterprise computing systems. It is also the most common operating system run by servers and other computers that form the bulk of the Internet. While you may never use UNIX on your local PC, you are using it indirectly, in one form or another, every time you log on to the ‘net.

While few people run UNIX on their own systems, there are in fact a number of different versions of UNIX available for the PC, and millions of PC users have chosen to install “UNIX” operating systems on their own desktop machines. There are dozens of variants of the basic UNIX interface; the most popular one for the PC platform is Linux,whichisitselfavailableinmanyflavors.WhileUNIXoperatingsystemscanbedifficulttosetupandrequiresomeknowledgetooperate,theyareverystableandrobust,areefficientwithsystemresourcesandaregenerallyfree or very inexpensive to obtain.

UNIXoperatingsystemsaredesignedtousethe“UNIXfilesystem”.Thephraseisinquotes,becausethereisnosingleUNIXfilesystem,anymorethanthereisasingleUNIXoperatingsystem.However,thefilesystemsusedbymostoftheUNIXoperatingsystemtypesouttherearefairlysimilar,andratherdistinctfromthefilesystemsused by other operating systems, such as DOS or Windows.

AsanoperatingsystemgearedspecificallyforuseonthePC,LinuxistheUNIXvariantthatgetsthemostattentionin PC circles. To improve its appeal, the programmers who are continually working to update and improve Linux have put into the operating system compatibility support for most of the other operating systems out there. Linux will read and write to FAT partitions, and with newer versions this includes FAT32.

6.5.1 MEMThis command displays amount of total available memory (low, Expanded and Extended) and all currently programs.Syntax: MEM [/f][/p][/m]

Switches:/f : Using this switch MEM display all the areas of memory that are fee./p : Use this option to display the information one screen at a time./m :Displayinformationabouthowaspecifiedprogramisusingmemory.

Example: MEM/p and then press <Enter>

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6.5.2 FILTERAPowerfulfeatureofDOSisitsuseoffilterstoprocessdatadirectly.ADOSFILTERcanprocessinuniquewayany data that passes through it and can change what we see on the screen.

There are three FILTERS include in DOS.MORE: More command used to pause vertical Scrolling on the display screen, after each screenful, The display •pauses and the message - - More - - appears. Pressing any key displays the next screen.EXAMPLE:C:\>MORE<TYPEFILE.TXTandthenpress<Enter>EXAMPLE: C:\> DIR /MORE and then press <Enter>SORT:Reads,SortsinOrderandsendsthedatatothescreen,fileortoanotherdevice.Sorttoarrangedatain•an order.SYNTAX:SORT[drive:][Path][filename][/r][+n]

Switches: [drive:][Path][filename] : Specifiesthenameandlocationofthefiletobesearches.Itmustbeprecededby the redirection character (<).[/r] : Sort lines in reverse ASCII Order ( Z-A)[+n] : Sorts line starting with the contents in column n. The default is 1.

EXAMPLE: C:\> SORT < NAME .TXT and then press <Enter>EXAMPLE: C:\> SORT /+20 < PHONE .TXT and then press <Enter>EXAMPLE: C:\> DIR / SORT > PHONE .TXT and then press <Enter>

Note:Sortcommanddoesn’tdistinguishbetweenupperandlowercase.Itcansortfileofmaximum63ksize.Combining Input & Output redirection:EXAMPLE: C:\> SORT < NAME .DAT > SORTNAME.DAT and then press <Enter>Here the sort command is being directed to take its input from <name.dat and after sorting, send its output to the>sortname.datfile.

FIND:ThefindFilterisusedtosearchafileoneormoredesignatedcharacter(calledatextstring)Depending•upon the form of the FIND Command. Each line having (or not having) the text string is sent to an output devices. SuchastheScreen,afileortheprinter.Thetextstringisalwaystypedwithinquotes(“TextSring”).SYNTAX:FIND[/v][/c][/n]“String“[d:][path][filename]Switches: [/v] : Displays all the lines that do not contain string.[/c] : Display the total number of lines found to contain the string.[/n] : Display the line number as well as the line that contains the string.[/i] : Ignores uppercase or lowercase during the search.

Where:“String” : Specifiesoneormorealphabetornumericcharacterwhosemaximumlengthshouldnotbe more than 250 characters and must be enclosed in double quotes.

[d:] [path][filename]: Specifies the name and location of the file to be searches EXAMPLE: C : \ > FIND “Rajni” my.txt per.txt and then press <Enter>EXAMPLE: C:\> DIR/ FIND “TXT” and then press <Enter>


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6.5.3 ATTRIBEvery File on the Disk has its own description like size, space occupied, the type, the date it was created, etc. Likewise,everyfilehasfewattributes.Theattributesofafileindicateswhetheritisa

Read-Only File: r•Archive File a•Hidden File: h•System File s•

WiththeATTRIBcommandyoucanchecktheattributesofafile.SYNTAX:ATTRIB[+r][+a][+h][/+s][filename]Switches:+r, -r : +r Read-Only attribute or, -r turn of Read-Only attribute+a,-a : +a archive attribute, or -a turn of archive attribute+h,-h : +h hidden attribute, or –h turn of hidden attribute+s, -s : +s system attribute and it should not be used generally

Note:WhileCreatinganewfileeveryfilegetsreadonlyattributeandarchiveattributebydefault.

EXAMPLE: C:\> ATTRIB my.txt +R and then press <Enter>EXAMPLE: C:\> ATTRIB my.txt +H and then press <Enter>

6.5.4 DELTREEThiscommandusedfordeletinganentiredirectorywhetherinthatdirectorycontainsfilesorsubdirectoriesandalsoitwilldeletehiddenfiles.Syntax: DELTREE [drive:][path] directories [/y]EXAMPLE: C:\> DELTREE my.txt and then press <Enter>

6.5.5 EDITThisistheDOSEditor,whichyoucanusetoeditthetextfileandalsocreatingnewfile.Syntax:Edit[drive:][path][filename]EXAMPLE: C:\> EDIT c:\sams\FO.TXT and then press <Enter>EXAMPLE: C:\> Edit NEW FILE and then press <Enter>

6.6 Batch FilesItisacollectionofDOScommandstoperformacertaintaskorabatchfileisnothingbutsequenceofcommandsto perform sequence of operations step by step. Look at the following commands you give step by step to perform an operation.

Suppose your job isFirst - Check the directorySecond- CopyafilecalledABC.txttoanotherdiskThird - Delete ABC.TXT from the present diskFourth - Clear the screen

If you do all this steps daily after your hour, then the commands you give would be:C:\> DIR <Enter>•C:\>COPYC:ABC.TXTD:<Enter>•C:\> DEL ABC.TXT <Enter>•C:\> CLS <Enter>•

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Instead of heating your head daily giving the same set of commands you can do it in a much simpler manner. All youdoisputallthecommandsinabatchfile.

Howtocreateabatchfile:C:\>COPYCONA.bat<Enter>

Note:HereConmeansConsolethatisKeyboard,Athefilenameand.batisextension.

Itiscompulsorythatabatchfilemusthaveextension.BAT.Youwillfindthecursorbelow‘A’nowtypeC:\> DIR <Enter>C:\>COPYA.TXTD:<Enter>C:\> DEL A.TXT <Enter>C:\> CLS <Enter>

NowPresstheF6orCtrl+Zkeycombination.Youshallfind^ZsymbolbelowCLS,NowpressEnter.Youwillreceivethefollowingmessage:1filesCopied.

And you are returned to the prompt C:\>

NowtoexecutetheBatchFilesimplytypethenameofthefile.C:\> A <Enter>

YouwillseeallthecommandsintheA.Batcomerightintoaction.Soinsteadoftypingallthosecommandoneafteranotherperformedthesamejobbyjusttypingthefilename.

6.7 Batch SystemSome computer systems only did one thing at a time. They had a list of the computer system may be dedicated to a single program until its completion, or they may be dynamically reassigned among a collection of active programs in different stages of execution. Batch operating system is one where programs and data are collected together in abatchbeforeprocessingstarts.Ajobispredefinedsequenceofcommands,programsanddatathatarecombinedin to a single unit called job.

Fig. 6.1 shows the memory layout for a simple batch system. Memory management in batch system is very simple. Memory is usually divided into two areas: Operating system and user program area.

Operating System

User Program Area

Resident Portion

Transient

Program

Fig. 6.2 Memory layout for a simple batch system


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Schedulingisalsosimpleinbatchsystem.Jobsareprocessedintheorderofsubmission,i.e.,firstcomefirstservedfashion. When job completed execution, its memory is releases and the output for the job gets copied into an output spoolforlaterprinting.Batchsystemoftenprovidessimpleformsoffilemanagement.Accesstofileisserial.Batchsystems do not require any time critical device management.

Batchsystemsareinconvenientforusersbecauseuserscannotinteractwiththeirjobstofixproblems.Theremayalso be long turnaround times. Example of this system is id generating monthly bank statement. Advantages of batch system are as follows:

Move much of the work of the operator to the computer.•Increasedperformancesinceitwaspossibleforjobtostartassoonasthepreviousjobfinished.•

Disadvantages of batch systemTurnaround time can be large from user standpoint.•Difficulttodebugprogram.•Ajobcouldenteraninfiniteloop.•A job could corrupt the monitor, thus affecting pending jobs.•Due to lack of protection scheme, one batch job can affect pending jobs.•

6.8 Time Sharing SystemsMulti-programmed batched systems provide an environment where the various system resources (for example, CPU, memory, peripheral devices) are utilised effectively. Time sharing, or multitasking, is a logical extension of multiprogramming. Multiple jobs are executed by the CPU switching between them, but the switches occur so frequently that the users may interact with each program while it is running.

An interactive, or hands-on, computer system provides on-line communication between the user and the system. The user gives instructions to the operating system or to a program directly, and receives an immediate response. Usually, a keyboard is used to provide input, and a display screen (such as a cathode-ray tube (CRT) or monitor) isusedtoprovideoutput.Ifusersaretobeabletoaccessbothdataandcodeconveniently,anon-linefilesystemmustbeavailable.Afileisacollectionofrelatedinformationdefinedbyitscreator.Batchsystemsareappropriatefor executing large jobs that need little interaction.

Time-sharing systems were developed to provide interactive use of a computer system at a reasonable cost. A time-shared operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time-shared computer; each user has at least one separate program in memory. A program that is loaded into memory and is executing is commonly referred to as a process. When a process executes, it typically executes for onlyashorttimebeforeiteitherfinishesorneedstoperformI/O.I/Omaybeinteractive;thatis,outputistoadisplay for the user and input is from a user keyboard. Since interactive I/O typically runs at people speeds, it may take a long time to complete.

A time-shared operating system allows the many users to share the computer simultaneously. Since each action or command in a time-shared system tends to be short, only a little CPU time is needed for each user. As the system switches rapidly from one user to the next, each user is given the impression that she has her own computer, whereas actually one computer is being shared among many users.

Time-sharing operating systems are even more complex than are multi-programmed operating systems. As in multiprogramming, several jobs must be kept simultaneously in memory, which requires some form of memory management and protection.

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6.9 MultiprogrammingWhen two or more programs are in memory at the same time, sharing the processor is referred to the multiprogramming operating system. Multiprogramming assumes a single processor that is being shared. It increases CPU utilisation by organising jobs so that the CPU always has one to execute. Fig. 4.3 shows the memory layout for a multiprogramming system.

Operating System

job 1

job 2

job 3

job 4

0

512M

Fig. 6.3 Memory layout for a multiprogramming system

The operating system keeps several jobs in memory at a time. This set of jobs is a subset of the jobs kept in the job pool. The operating system picks and begins to execute one of the jobs in the memory. Multi-programmed system provides an environment in which the various system resources are utilised effectively, but they do not provide for user interaction with the computer system.

Jobs entering into the system are kept into the memory. Operating system picks the job and begins to execute one of the jobs in the memory. Having several programs in memory at the same time requires some form of memory management. Multiprogramming operating system monitors the state of all active programs and system resources. This ensures that the CPU is never idle unless there are no jobs.

AdvantagesHigh CPU utilisation.•It appears that many programs are allotted CPU almost simultaneously.•

DisadvantagesCPU scheduling is requires.•To accommodate many jobs in memory, memory management is required.•


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6.10 SpoolingSpooling is an acronym for simultaneous peripheral operations on line. Spooling refers to putting jobs in a buffer, a special area in memory or on a disk where a device can access them when it is ready. Spooling is useful because device access data that different rates. The buffer provides a waiting station where data can rest while the slower device catches up. Fig 2.3 shows the spooling.

DISK

CARD READER PRINTER

Fig. 6.4 Spooling

Computer can perform I/O in parallel with computation; it becomes possible to have the computer read a deck of cards to a tape, drum or disk and to write out to a tape printer while it was computing. This process is called spooling.

The most common spooling application is print spooling. In print spooling, documents are loaded into a buffer and then the printer pulls them off the buffer at its own rate. Spooling is also used for processing data at remote sites. The CPU sends the data via communications path to a remote printer. Spooling overlaps the I/O of one job with thecomputationofotherjobs.Onedifficultywithsimplebatchsystemsisthatthecomputerstillneedstoreadthedecks of cards before it can begin to execute the job. This means that the CPU is idle during these relatively slow operations.Spoolingbatchsystemswerethefirstandarethesimplestofthemultiprogrammingsystems.

Advantage of SpoolingThe spooling operation uses a disk as a very large buffer.•Spooling is however capable of overlapping I/O operation for one job with processor operations for another •job.

6.11 Essential Properties of the Operating System BatchJobs with similar needs are batched together and run through the computer as a group by an operator or automatic job sequencer. Performance is increased by attempting to keep CPU and I/O devices busy at all times through buffering, off line operation, spooling and multiprogramming. A Batch system is good for executing large jobs that need little interaction; it can be submitted and picked up latter.

6.11.1 Time SharingIt uses CPUs scheduling and multiprogramming to provide economical interactive use of a system. The CPU switches rapidly from one user to another, i.e., the CPU is shared between a numbers of interactive users. Instead of having ajobdefinedbyspooledcardimages,eachprogramreadsitsnextcontrolinstructionsfromtheterminalandoutputis normally printed immediately on the screen.

6.11.2 InteractiveUser is on line with computer system and interacts with it via an interface. It is typically composed of many short transactions where the result of the next transaction may be unpredictable. Response time needs to be short since the user submits and waits for the result.

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6.11.3 Real time systemReal time systems are usually dedicated, embedded systems. They typically read from and react to sensor data. The systemmustguaranteeresponsetoeventswithinfixedperiodsoftimetoensurecorrectperformance.

6.11.4 DistributedIt distributes computation among several physical processors. The processors do not share memory or a clock. Instead, each processor has its own local memory. They communicate with each other through various communication lines.


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SummaryAn operating system acts as an intermediary between the user of a computer and computer hardware.•An operating system is software that manages the computer hardware.•An Operating system is concerned with the allocation of resources and services, such as memory, processors, •devices and information.Every general purpose computer consists of the hardware, operating system, system programs and application •programs.In the early days of micro computing, memory space was often limited, so the disk operating system was an •extension of the operating system.In the early days of computers, there were no disk drives; delay lines, punched cards, paper tape, magnetic tape, •magnetic drums, were used instead.DOS is an Operating System. It works as an interpreter between user and computer.•Process that starts up a computer is called booting.•TheinternalcommandscanexecuteimmediatelybutExternalCommandsrequirespecialfilesfortheirexecution•without which it is not possible to execute them.Dos can remember only the last command you had entered.•UNIX is one of the very oldest operating systems in the computer world, and is still widely used today.•AsanoperatingsystemgearedspecificallyforuseonthePC,LinuxistheUNIXvariantthatgetsthemost•attention in PC circles.Batch operating system is one where programs and data are collected together in a batch before processing •starts.Ajobispredefinedsequenceofcommands,programsanddatathatarecombinedintoasingleunitcalled•job.Multi-programmed batched systems provide an environment where the various system resources (for example, •CPU, memory, peripheral devices) are utilised effectively.An interactive, or hands-on, computer system provides on-line communication between the user and the •system.Time-sharing systems were developed to provide interactive use of a computer system at a reasonable cost.•When two or more programs are in memory at the same time, sharing the processor is referred to the •multiprogramming operating system.Spooling is useful because device access data that different rates.•

ReferencesBhatt, C. P., 2003. • An Introduction to Operating Systems: Concepts and Practice, 3rd ed. PHI Learning Pvt. Ltd.Kifer, M. & Smolka, S., 2007. • Introduction to Operating System Design and Implementation: The OSP 2 Approach, Springer.DISK OPERATING SYSTEM (DOS)• [Pdf] Available at: <http://computerbabu.webs.com/-%20New%20Folder/DISK%20OPERATING%20SYSTEM%20(DOS).pdf>[Accessed22May2013].Bhor, H., Rote, U. & Shinde, U., • Operating System [Pdf] Available at: <http://mu.ac.in/myweb_test/MCA%20study%20material/OS%20-%20PDF.pdf> [Accessed 22 May 2013].Murphy, M., 2011. • Introduction to Operating Systems [Video online] Available at: <http://www.youtube.com/watch?v=MzVGL44eq9w> [Accessed 22 May 2013].Learn Introduction to O S from the Fundamentals of Operating Systems• [Video online] Available at: <http://www.youtube.com/watch?v=cP-OPjwag4E> [Accessed 22 May 2013].

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Recommended ReadingBhatt, 2007. • Introduction To Operating Systems: Concepts And Practice An 2Nd Ed., 2nd ed. PHI Learning Pvt. Ltd.Johnson, P., 2004. • Introduction To Operating Systems, iUniverse.Jaeger, T., 2008. • Operating Systems Security, Morgan & Claypool Publishers.


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Self AssessmentAn ___________ is a program that controls the execution of application programs and acts as an interface 1. between the user of a computer and the computer hardware.

Operating systema. Hardwareb. Softwarec. Functiond.


MS-DOS1. Turning on the computerA.

Cold Booting2. Ctrl+Alt+DelB.

Warm Booting3. COMMAND.COMC.

Secondary name4. 3 or less than 3 charactersD. 1-A, 2-D, 3-B, 4-Ca. 1-C, 2-A, 3-B, 4-Db. 1-B, 2-C, 3-A, 4-Dc. 1-D, 2-B, 3-C, 4-Ad.

Which of the following statements is false?3. A command can be given in Capitals or Small letters also.a. All O/S has its own edition number or release or version number.b. The internalcommandscanexecute immediatelybutExternalCommandsrequirespecialfiles for theirc. execution without which it is not possible to execute them.DIR is used to display volume label and serial number of the current drive.d.

________ displays the current system time and prompt for entering new time.4. DATEa. TIMEb. CLSc. DIRd.

_________ command allows changing present directory to another directory.5. MKDIRa. PATHb. CHDIRc. RDd.

Whichcommandisusedtomakeduplicatefilesofanexistingfile?6. CUTa. COPYb. PASTEc. DUPLICATEd.

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ERASE1. DisplaydirectorystructureofaspecifieddirectorygraphicallyA.

REN2. Customise the dos promptB.

PROMPT3. ChangethenameofthefileordirectoryC.

TREE4. RemovesoneormorefilesfromthediskorcurrentworkingdirectoriesD. 1-B, 2-A, 3-C, 4-Da. 1-A, 2-B, 3-D, 4-Cb. 1-D, 2-C, 3-B, 4-Ac. 1-C, 2-D, 3-A, 4-Bd.

Which of the followings is not an external command?8. FCa. Doskeyb. Memc. VERd.

Which of the followings is not an internal command?9. COPYCONa. TYPEb. FILTERc. DELd.

_________ command displays amount of total available memory (low, Expanded and Extended) and all currently 10. programs.

MEMa. FILTERb. ATTRIBc. DELTREEd.


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Chapter VII

Data processing

Aim


introduce data processing•

elucidate architecture of computer system•

enlist types of data•

Objectives


explain data capturing •

explicateorganisationofrelativefile•

definedataandinformation•

Learning outcome


analysevariousoperationsperformedonfiles•

describe CPU organisation•

understandfileorganisation•

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7.1 IntroductionData processing is any computer process that converts data into information. The processing is usually assumed to be automated and running on a mainframe, minicomputer, microcomputer, or personal computer. Because data are most useful when well-presented and actually informative, data processing systems are often referred to as information systems to emphasise their practicality. Nevertheless, both terms are roughly synonymous, performing similar conversions; data-processing systems typically manipulate raw data into information, and likewise information systems typically take raw data as input to produce information as output.

To better market their profession, a computer programmer or a systems analyst that might once have referred, such as during the 1970s, to the computer systems that they produce as data-processing systems more often than not nowadays refers to the computer systems that they produce by some other term that includes the word information, such as information systems, information technology systems, or management information systems.

Inthecontextofdataprocessing,dataaredefinedasnumbersorcharactersthatrepresentmeasurementsfromtherealworld. A single datum is a single measurement from the real world. Measured information is then algorithmically derivedand/orlogicallydeducedand/orstatisticallycalculatedfrommultipledata.Informationisdefinedaseithera meaningful answer to a query or a meaningful stimulus that can cascade into further queries.

More generally, the term data processing can apply to any process that converts data from one format to another, although data conversion would be the more logical and correct term. From this perspective, data processing becomes the process of converting information into data and also the converting of data back into information. The distinction is that conversion doesn’t require a question (query) to be answered.

For example, information in the form of a string of characters forming a sentence in English is converted or encoded from a keyboard’s key-presses as represented by hardware oriented integer codes into ASCII integer codes after which it may be more easily processed by a computer not as merely raw, amorphous integer data, but as a meaningful characterinanaturallanguage’ssetofgraphemesandfinallyconvertedordecodedtobedisplayedascharacters,represented by a font on the computer display. In that example we can see the stage-by-stage conversion of the presence of and then absence of electrical conductivity in the key-press and subsequent release at the keyboard from raw substantially meaningless integer hardware-oriented data to evermore-meaningful information as the processing proceeds toward the human being.

A more conventional example of the established practice of using the term data processing is that a business has collected numerous data concerning an aspect of its operations and that this multitude of data must be presented in meaningful, easy-to-access presentations for the managers who must then use that information to increase revenue or to decrease cost. That conversion and presentation of data as information is typically performed by a data processing application.

When the domain from which the data are harvested is a science or engineering, data processing and information systems are considered too broad of terms and the more specialised term data analysis is typically used, focusing on the highly-specialised and highly-accurate algorithmic derivations and statistical calculations that are less often observed in the typical general business environment. This divergence of culture is exhibited in the typical numerical representations used in data processing versus numerical; data processing’s measurements are typically represented byintegersorbyfixedpointorbinary-codeddecimalrepresentationsofrealnumberswhereasthemajorityofdataanalysis’smeasurementsareoftenrepresentedbyfloatingpointrepresentationofrealnumbers.

Practically all naturally occurring processes can be viewed as examples of data processing systems where “real world” information in the form of pressure, light, etc. are converted by human observers into electrical signals in the nervous system as the senses we recognise as touch, sound, and vision. Even the interaction of non-living systems may be viewed in this way as rudimentary information processing systems. Conventional usage of the terms data processing and information systems restricts their use to refer to the algorithmic derivations, logical deductions, and statistical calculations that recur perennially in general business environments, rather than in the more expansive sense of all conversions of real-world measurements into real world information in, say, an organic biological system orevenascientificorengineeringsystem.


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7.1.1 DataData are any facts, numbers, or text that can be processed by a computer. Today, organisations are accumulating vast and growing amounts of data in different formats and different databases. This includes:

operational or transactional data such as, sales, cost, inventory, payroll, and accounting•non-operational data, such as industry sales, forecast data, and macro economic data•metadata-dataaboutthedataitself,suchaslogicaldatabasedesignordatadictionarydefinitions•

7.1.2 InformationThe patterns, associations, or relationships among all this data can provide information. For example, analysis of retail point of sale transaction data can yield information on which products are selling and when.

7.1.3 Types of DataThink about any collected data that you have experience of; for example, weight, sex, ethnicity, job grade, and consider their different attributes. These variables can be described as categorical or quantitative. The table summarises data types and their associated measurement level, plus some examples. It is important to appreciate that appropriate methods for summary and display depend on the type of data being used. This is also true for ensuring the appropriate statistical test is employed.

Type of Data Level of Measurement Examples

Categorical

Nominal (no inherent order in categories) Eye color, ethnicity, diagnosis

Ordinal (categories have inherent order) Job grade, age groups

Binary (2 categories – special case of above) Gender

Quantitative (Interval/Ratio) (NB units of measurement used)

Discrete (usually whole numbers) Size of household (ratio)

Continuous (can, in theory, take any value in a range, although necessarily recorded to a predetermined degree of precision)

Temperature °C/°F (no absolute zero) (interval) Height, age (ratio)

Table 7.1 Types of Data

7.2 Input, Processing and outputWhenever a computer is used it must work its way through three basic stages before any task can be completed. These are input, processing and output. A Computer works through these stages by running a program. A program is a set of step-by-step instructions which tells the computer exactly what to do with the input in order to produce the required output.

7.2.1 InputThe input stage of computing is concerned with getting the data needed by the program into the computer. Input devices are used to do this. The most commonly used input devices are the mouse and the keyboard.

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7.2.2 ProcessingThe program contains instructions about what to do with the input. During the processing stage the compute follows these instructions using the data which has just been input. What the computer produces at the end of this stage, the output, will only be as good as the instructions given in the program. In other words if garbage has been put in to the program, garbage is what will come out of the computer. This is known as GIGO, or Garbage in Garbage Out.

7.2.3 OutputThe output stage of computing is concerned with giving out processed data as information in a form that is useful to the user. Output devices are used to do this. The most commonly used output devices are the screen, which is also called a monitor or VDU and the printer.

7.3 Architecture of Computer SystemThis is the ‘brain’ of the computer. It is where all the searching, sorting, calculating and decision making takes place. The CPU collects all of the raw data from various input devices (such a keyboard or mouse) and converts it into useful information by carrying out software instructions. The result of all that work is then sent to output devices such as monitors and printers.

The CPU is a microprocessor - a silicon chip - composed of tiny electrical switches called ‘transistors’. The speed at which the processor carries out its operations is measured in megahertz (MHz) or Gigahertz (GHz). The higher the number of MHz the faster the computer can process information. A common CPU today runs at around 3 GHz or more. The Intel Pentium processor and the Athlon are examples of a CPU.

PARTS OF A CPU

Inputs and Outputs

Control Unit

Backing Store

Immediate AccessStore

ARITHMETIC& LOGIC

UNIT(ALU)

Fig. 7.1 Block diagram of CPU

7.3.1 The Control Unit (CU)The Control Unit (CU) co-ordinates the work of the whole computer system and it has three main jobs:

It controls the hardware attached to the system. The Control Unit monitors the hardware to make sure that the •commands given to it by the current program are activated.It controls the input and output of data, so all the signals go to the right place at the right time.•ItcontrolstheflowofdatawithintheCPU.•


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7.3.2 The Immediate Access Store (IAS)The Immediate Access Store (IAS) holds the data and programs needed at that instant by the Control Unit. The CPU reads data and programs kept on the backing storage and store them temporarily in the IAS’s memory. The CPU needs to do this because Backing Store is much too slow to be able to run data and programs from directly. For example, let’s pretend that a modern CPU was slowed down to carry out one instruction in 1 second, then the harddisk(i.e.,BackingStore)wouldtake3monthstosupplythedataitneeds!Sothetrickistocallinenoughofthe data and programs into fast Immediate Access Store memory so as to keep the CPU busy.

7.3.3 ALU stands for Arithmetic and Logic Unit.It is where the computer processes data by either manipulating it or acting upon it. It has two parts:

Arithmetic part - does exactly what you think it should - it does the calculations on data such as 3 + 2.•Logic part - This section deals with carrying out logic and comparison operations on data. For example working •out if one data value is bigger than another data value.

7.4 Concepts of FilesAcomputerfileisapieceofarbitraryinformation,orresourceforstoringinformation,thatisavailabletoacomputerprogramandisusuallybasedonsomekindofdurablestorage.Afileisdurableinthesensethatitremainsavailableforprogramstouseafterthecurrentprogramhasfinished.Computerfilescanbeconsideredasthemoderncounterpartofthefilesofprinteddocumentsthattraditionallyexistedinofficesandlibraries.

7.4.1 File contentsAsfarastheoperatingsystemisconcerned,afileisinmostcasesjustasequenceofbinarydigits.Atahigherlevel,wherethecontentofthefileisbeingconsidered,thesebinarydigitsmayrepresentintegervaluesortextcharacters,Itisuptotheprogramusingthefiletounderstandthemeaningandinternallayoutofinformationinthefileandpresentittoauserasadocument,image,song,orprogram.Atanyinstantintime,afilehasmighthaveasize,normallyexpressedinbytes,thatindicateshowmuchstorageisassociatedwiththefile.

Informationinacomputerfilecanconsistofsmallerpacketsofinformation(oftencalledrecordsorlines)thatareindividuallydifferentbutsharesometraitincommon.Forexample,apayrollfilemightcontaininformationconcerningalltheemployeesinacompanyandtheirpayrolldetails;eachrecordinthepayrollfileconcernsjustone employee, and all the records have the common trait of being related to payroll this is very similar to placing all payrollinformationintoaspecificfilingcabinetinanofficethatdoesnothaveacomputer.Atextfilemaycontainlines of text, corresponding to printed lines on a piece of paper.

Thewayinformationisgroupedintoafileisentirelyuptothepersondesigningthefile.Thishasledtoaplethoraofmoreorlessstandardisedfilestructuresforallimaginablepurposes,fromthesimplesttothemostcomplex.Mostcomputerfilesareusedbycomputerprograms.Theseprogramscreate,modifyanddeletefilesfortheirownuseonanas-neededbasis.Theprogrammerswhocreatetheprogramsdecidewhatfilesareneeded,howtheyareto be used and (often) their names.

Insomecases,computerprogramsmanipulatefilesthataremadevisibletothecomputeruser.Forexample,inaword-processingprogram,theusermanipulatesdocumentfilesthatshenamesherself.Thecontentofthedocumentfileisarrangedinawaythattheword-processingprogramunderstands,buttheuserchoosesthenameandlocationofthefile,andsheprovidesthebulkoftheinformation(suchaswordsandtext)thatwillbestoredinthefile.

Filesonacomputercanbecreated,moved,modified,grown,shrunkanddeleted.Inmostcases,computerprogramsthatareexecutedonthecomputerhandletheseoperations,buttheuserofacomputercanalsomanipulatefilesifnecessary.Forinstance,MicrosoftWordfilesarenormallycreatedandmodifiedbytheMicrosoftWordprograminresponsetousercommands,buttheusercanalsomove,rename,ordeletethesefilesdirectlybyusingafilemanagerprogram such as Windows Explorer (on Windows computers).

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7.4.2OperationsonthefileTheoperationswhichareperformedonthefileareasfollows:

Openingafiletouseitscontents•Reading or updating the contents•Committing updated contents to durable storage•Closingthefile,therebylosingaccessuntilitisopenedagain•

7.4.3 File OrganisationTherearevariouskindsoffilesandeachhasitsownkindoforgnisation.Thesefileorganisationsareexplainedbelow:Sequential FileAccesstorecordsinaSequentialfileisserial.Toreachaparticularrecord,alltheprecedingrecordsmustberead.As we observed when the topic was introduced earlier in the course, the organisation of an unordered Sequential filemeansitisonlypracticaltoreadrecordsfromthefileandaddrecordstotheendofthefile(OPEN..EXTEND).It is not practical to delete or update records. While it is possible to delete, update and insert records in an ordered sequentialfile,theseoperationshavesomedrawbacks.

ProblemsaccessingorderedSequentialfilesRecordsinanorderedsequentialfilearearranged,inorder,onsomekeyfieldorfields.Whenwewanttoinsert,deleteoramendarecordwemustpreservetheordering.Theonlywaytodothisistocreateanewfile.Inthecaseofaninsertionorupdate,thenewfilewillcontaintheinsertedorupdatedrecord.Inthecaseofadeletion,thedeletedrecordwillbemissingfromthenewfile.

Themaindrawbacktoinserting,deletingoramendingrecordsinanorderedsequentialfileisthattheentirefilemustbereadandthentherecordswrittentoanewfile.Sincediskaccessisoneoftheslowestthingswecandoincomputing this is very wasteful of computer time when only a few records are involved. For instance, if 10 records aretobeinsertedintoa10,000recordfile,then10,000recordswillhavetobereadfromtheoldfileand10,010writtentothenewfile.Theaveragetimetoinsertanewrecordwillthusbeverygreat.

InsertingrecordsinanorderedSequentialfileToinsertarecordinanorderedSequentialfile:

All the records with a key value less than the record to be inserted must be read and then written to the new •file.Thentherecordtobeinsertedmustbewrittentothenewfile.•Finally,theremainingrecordsmustbewrittentothenewfile.•

DeletingrecordsfromanorderedSequentialfileTodeletearecordinanorderedSequentialfile:

Alltherecordswithakeyvaluelessthantherecordtobedeletedmustbewrittentothenewfile.•Whentherecordtobedeletedisencountereditisnotwrittentothenewfile.•Finally,alltheremainingrecordsmustbewrittentothenewfile.•

AmendingrecordsinanorderedSequentialfileToamendarecordinanorderedSequentialfile:

All the records with a key value less than the record to be amended must be read and then written to the new •file.Then the record to be amended must be read the amendments applied to it and the amended record must then •bewrittentothenewfile.Finally,alltheremainingrecordsmustbewrittentothenewfile.•


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7.4.4 Relative FileAswehavealreadynoted,theproblemwithsequentialfilesisthataccesstotherecordsisserial.Toreachaparticularrecord,alltheproceedingrecordsmustberead.Directaccessfilesallowdirectaccesstoaparticularrecordinthefileusing a key and this greatly facilitates the operations of reading, deleting, updating and inserting records. COBOL supportstwokindsofdirectaccessfileorganisations-RelativeandIndexed.

OrganisationofRelativefilesRecordsinrelativefilesareorganisedonascendingrelativerecordnumber.ARelativefilemaybevisualisedasaonedimensiontablestoredondisk,wheretherelativerecordnumberistheindexintothetable.Relativefilessupport sequential access by allowing the active records to be read one after another.

RelativeRecordNumber

1 Rec001

2 free

3 Rec003

4 Rec004

5 free

6 free

7 Rec007

325 Rec325

326 Rec326

327 free

328 Rec328

Fig. 7.2 Relative File - Organisation

Relativefilessupportonlyonekey.Thekeymustbenumericandmusttakeavaluebetween1andthecurrenthighestrelativerecordnumber.Enoughroomisallocatedtothefiletocontainrecordswithrelativerecordnumbersbetween 1 and the highest record number.

For instance, if the highest relative record number used is 10,000 then room for 10,000 records is allocated to the file.Figure1belowcontainsaschematicrepresentationofaRelativefile.Inthisexample,enoughroomhasbeenallocated on disk for 328 records. But although there is room for 328 records in the current allocation, not all the record locations contain records. The record areas labeled “free”, have not yet had record values written to them.

AccessingrecordsinaRelativefileToaccessarecordinaRelativefileaRelativeRecordNumbermustbeprovided.Supplyingthisnumberallowstherecordtobeaccesseddirectlybecausethesystemcanusethestartpositionofthefileondisk,thesizeoftherecord,and the relative record number to calculate the position of the record.

BecausethefilemanagementsystemonlyhastomakeafewcalculationstofindtherecordpositiontheRelativefileorganisationisthefasterofthetwodirectaccessfileorganisationsavailableinCOBOL.Itisalsothemoststorageefficient.

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7.4.5 Indexed FilesWhiletheusefulnessofaRelativefileisconstrainedbyitsrestrictivekey,Indexedfilessufferfromnosuchlimitation.Indexedfilesmayhaveupto255keys,thekeyscanbealphanumericandonlytheprimarykeymustbeunique.Inaddition,itispossibletoreadanIndexedfilesequentiallyonanyofitskeys.

OrganisationofIndexedfilesAnindexedfilemayhavemultiplekeys.Thekeyuponwhichthedatarecordsareorderediscalledtheprimarykey.Theotherkeysarecalledalternatekeys.RecordsintheIndexedfilearesequencedonascendingprimarykey.Overtheactualdatarecords,thefilesystembuildsanindex.Whendirectaccessisrequired,thefilesystemusesthisindextofind,read,insert,updateordeletetherequiredrecord.

ForeachofthealternatekeysspecifiedinanIndexedfile,analternateindexisbuilt.However,thelowestlevelofanalternate index does not contain actual data records. Instead, this level made up of base records which contain only the alternate key value and a pointer to where the actual record is. These base records are organised in ascending alternate key order. As well as allowing direct access to records on the primary key or any of the 254 alternate keys, indexedfilesmayalsobeprocessedsequentially.Whenprocessedsequentially,therecordsmaybereadinascendingorder on the primary key or on any of the alternate keys.

Sincethedatarecordsareinheldinascendingprimarykeysequenceitiseasytoseehowthefilemaybeaccessedsequentially on the primary key. It is not quite so obvious how sequential on the alternate keys is achieved. This is coveredintheunitonIndexedfiles.

Organizingfilesandfloders

(root)

Payroll

Salaries

Logfile

Widgets

Foobar

Employees

Timecards

Managers

Leads

Clerks

Fig. 7.3 Files and folders arranged in a hierarchy

Inmoderncomputersystems,filesaretypicallyaccessedusingnames.Insomeoperatingsystems,thenameisassociatedwiththefileitself.Inothers,thefileisanonymous,andispointedtobylinksthathavenames.Inthelattercase,ausercanidentifythenameofthelinkwiththefileitself,butthisisafalseanalogue,especiallywherethereexistsmorethanonelinktothesamefile.


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Files(orlinkstofiles)canbelocatedindirectories.However,moregenerally,adirectorycancontaineitheralistoffiles,oralistoflinkstofiles.Withinthisdefinition,itisofparamountimportancethattheterm“file”includesdirectories.Thispermitstheexistenceofdirectoryhierarchies.Anamethatreferstoafilewithinadirectorymustbe unique. In other words, there must be no identical names in a directory. However, in some operating systems, anamemayincludeaspecificationoftypethatmeansadirectorycancontainanidenticalnametomorethanonetypeofobjectsuchasadirectoryandafile.

Inenvironmentsinwhichafileisnamed,afile’snameandthepathtothefile’sdirectorymustuniquelyidentifyitamongallotherfiles in thecomputersystemno twofilescanhave thesamenameandpath.Whereafile isanonymous, named references to it will exist within a namespace. In most cases, any name within the namespace willrefertoexactlyzerooronefile.However,anyfilemayberepresentedwithinanynamespacebyzero,oneormorenames.Anystringofcharactersmayormaynotbeawell-formednameforafileoralinkdependinguponthe context of application. Whether or not a name is well formed depends on the type of computer system being used.Earlycomputerspermittedonlyafewlettersordigitsinthenameofafile,butmoderncomputersallowlongnames (some up to 255) containing almost any combination of unicode letters or unicode digits, making it easier to understandthepurposeofafileataglance.Somecomputersystemsallowfilenamestocontainspaces;othersdonot.Suchcharacterssuchas/or\areforbidden.Case-sensitivityoffilenamesisdeterminedbythefilesystem.

Mostcomputersorganisefiles intohierarchiesusing folders,directories,orcatalogs. (Theconcept is thesameirrespectiveoftheterminologyused.)Eachfoldercancontainanarbitrarynumberoffiles,anditcanalsocontainotherfolders.Theseotherfoldersarereferredtoassubfolders.Subfolderscancontainstillmorefilesandfoldersand so on, thus building a tree-like structure in which one “master folder” (or “root folder” — the name varies from oneoperatingsystemtoanother)cancontainanynumberoflevelsofotherfoldersandfiles.Folderscanbenamedjustasfilescan(exceptfortherootfolder,whichoftendoesnothaveaname).Theuseoffoldersmakesiteasiertoorganisefilesinalogicalway.

7.5 Protecting FilesManymoderncomputersystemsprovidemethodsforprotectingfilesagainstaccidentalanddeliberatedamage.Computersthatallowformultipleusersimplementfilepermissionstocontrolwhomayormaynotmodify,delete,orcreatefilesandfolders.Agivenusermaybegrantedonlypermissiontomodifyafileorfolder,butnottodeleteit;orausermaybegivenpermissiontocreatefilesorfolders,butnottodeletethem.Permissionsmayalsobeusedtoallowonlycertainuserstoseethecontentsofafileorfolder.Permissionsprotectagainstunauthorisedtamperingordestructionofinformationinfiles,andkeepprivateinformationconfidentialbypreventingunauthorisedusersfromseeingcertainfiles.

Anotherprotectionmechanismimplementedinmanycomputersisaread-onlyflag.Whenthisflagisturnedonforafile(whichcanbeaccomplishedbyacomputerprogramorbyahumanuser)thefilecanbeexamined,butitcannotbemodified.Thisflagisusefulforcriticalinformationthatmustnotbemodifiedorerased,suchasspecialfilesthatareusedonlybyinternalpartsofthecomputersystem.Somesystemsalsoincludeahiddenflagtomakecertainfilesinvisible;thisflagisusedbythecomputersystemtohideessentialsystemfilesthatusersmustnevermodify.

7.6StoringfilesInphysicalterms,mostcomputerfilesarestoredonharddisksspinningmagneticdisksinsideacomputerthatcanrecordinformationindefinitely.Harddisksallowalmostinstantaccesstocomputerfiles.Onlargecomputers,somecomputerfilesmaybestoredonmagnetictape.Filescanalsobestoredonothermediainsomecases,suchas writeable compact discs, Zip drives, etc.

7.6.1BackingupfilesWhencomputerfilescontaininformationthatisextremelyimportant,abackupprocessisusedtoprotectagainstdisastersthatmightdestroythefiles.Backingupfilessimplymeansmakingcopiesofthefilesinaseparatelocationso that they can be restored if something happens to the computer, or if they are deleted accidentally.

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Therearemanywaystobackupfiles.Mostcomputersystemsprovideutilityprogramstoassistintheback-upprocess,whichcanbecomeverytimeconsumingiftherearemanyfilestosafeguard.FilesareoftencopiedtoremovablemediasuchaswriteableCDsorcartridgetapes.Copyingfilestoanotherharddiskinthesamecomputerprotectsagainst failure of one disk, but if it is necessary to protect against failure or destruction of the entire computer, then copiesofthefilesmustbemadeonothermediathatcanbetakenawayfromthecomputerandstoredinasafe,distant location.

7.7 File TerminologyThereareafewtermsthatyouneedtounderstandwhenlearningaboutfilesystem.Thesewillbeexplainedoverthenextcoupleofpages.Filecanstoredataorinformationinvariousformats.Supposeinafiledataisstoredinthe tables just like the one below:

First Name Last Name Address City Age

Mickey Mouse 123 Fantasy Way Anaheim 73

Bat Man 321 Cavern Ave Gotham 54

Wonder Woman 987 Truth Way Paradise 39

Donald Duck 555 Quack Street Mallard 65

Bugs Bunny 567 Carrot Street Rascal 58

Wiley Coyote 999 Acme Way Canyon 61

Cat Woman 234 Purrfect Street Hairball 32

Tweety Bird 543 Itotltaw 28

Table 7.2 File terminology

7.7.1 RecordsAs you saw previously, each table stores can hold a great deal of data. Each table contains a lot of records. A record is all of the data or information about one person or one thing. In the table below, all of the information about each cartoon character is stored in a ‘row’ or record.










Records

Table 7.3 Records


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WhatinformationcouldyoufindintherecordforCatWoman?What do you think the database at your school stores records about?How about the library? What records would be stored on that database?

7.7.2 FieldsEach table contains a lot of records. A record is made up of lots of individual pieces of information. Look at Wonder Woman’srecord;itstoresherfirstname,lastname,address,cityandage.Eachoftheseindividualpiecesofinformationinarecordarecalleda‘field’A‘field’isonepieceofdataorinformationaboutapersonorthing.

Fields










Table 7.4 Fields

WhatfieldscanyoufindaboutTweetyBird?Whatfieldsdoyouthinkwouldbestoredinyourstudentrecordontheschooldatabase?Whatfieldswouldbestoredinabookrecordinthelibrarydatabase?

7.8 Data CapturingAny database or information system needs data entered into it, in order for it to be of any use. There are many methods which can be used to collect and enter data, some manual, and some automatic. We will also look in particular detail at designing an effective paper-based data capture form.

7.8.1 Direct Data CapturingHere are some of the methods that can be used to capture data directly.

Barcode readerA bar code reader uses visible red light to scan and ‘read’ the barcode. As the red light shines across the light and dark bandsofthebarcode,sothereflectedredlightisalsolighteranddarker(doyouseethatonthepictureopposite?)TheHandScannersensesthereflectedlightandtranslatesitintodigitaldata.Thedigitaldataistheninputintothecomputer.Thecomputermaydisplaytheresultsonascreenandalsoinputitintothecorrectfieldsinthedatabase.Typical uses:

Shop-tofinddetailsontheproductsoldandprice•Library - record the ISBN number of the book and the borrower’s card number•Warehouse - to check the labels on boxes delivered against what is recorded on the delivery sheet.•

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Magnetic ink character recognition (MICR)The numbers at the bottom of a cheque are written in a special ink which contains iron particles. This ink is magnetised and commonly called ‘magnetic ink’. It can be read by a special machine called a Magnetic Ink Character Reader (MICR).

Optical mark readers (OMR)An Optical Mark Reader is a scanning device that reads carefully placed pencil marks on a specially designed form or document. A simple pen or pencil mark is made on the form to indicate the correct choice e.g. a multiple choice exam paper or on the National Lottery ticket selection form.

The completed forms are scanned by an Optical Mark Reader (OMR) which detects the presence of a mark by measuringthereflectedlight.Lesslightisreflectedwhereamarkhasbeenmade.TheOMRtheninterpretsthepattern of marks into a data record and sends this to the computer for storage, analysis and reporting. This provides a very fast and accurate method of inputting large amounts of data, provided the marks have been made accurately and clearly.

Optical character recognition (OCR)Optical Character Recognition (OCR) enables the computer to identify written or printed characters. An OCR system consists of a normal scanner and some special software. The scanner is used to scan the text from a document into the computer. The software then examines the page and extracts the text from it, storing it in a form that can be edited or processed by normal word processing software. The ability to scan the characters accurately depends on how clear the writing is. Scanners have been improved to be able to read different styles and sizes of text as well as neat handwriting. Although they are often up to 95% accurate, any text scanned with OCR needs careful checking because some letters can be misread. OCR is also used to automatically recognise postcodes on letters at sorting offices.

Speech RecognitionThe user talks into a microphone. The computer ‘listens’ to the speaker, then translates that information to written words and phrases. It then displays the text on to the monitor. This process happens immediately, so as you say the words, they appear on the screen. The software often needs some “training” in order for it to get used to your voice, but after that it is simple to use.

7.8.2 Data Capture FormsAlthough there are many methods of capturing data automatically, many businesses prefer to capture it manually.

Paper-based data capture formsThisisthemostcommonlyusedmethodofcollectingorcapturingdata.Peoplearegivenaformtofillinwiththeirpersonal details, e.g. name, address, telephone number, date of birth etc. Once the form is completed, it is given to a member of staff who will enter the data from it, into a database or information system.

Computerised data entry formsA member of staff could type the information directly into a computerised data entry form whilst the customer is with them. They ask the question in the order it appears on the form and enter the answer using a keyboard. More commonly though, the details will be typed in by copying what was written on the paper-based data capture form. Whenthismethodisused,itisimportantthatthefieldsonbothformsarelaidoutinthesameordertospeeduptheprocess of entering the data.

Designing Data Capture FormA data capture form looks simple enough to design, don’t you just type out a few questions, put a couple of boxes forcustomerstofillintheirinformationandthenprintitout?No,it’snotassimpleasthat.Ifyouwanttocollectgood quality data, you need to think carefully about the design of the form. All forms should have the name of the organisation at the top.


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GREYSIDE YOUTH CLUB

Memebership Application Form

Please complete the top section of this membership apliccation form. Then send the form toTheYouthClub,15GreysidePark,Liverpool,Merseyside, L2 3XJ.

Fig. 7.4 Sample data capture form

They should also have an explanation to tell the customer what the form is for, in this case ‘membership application form’, or ‘data collection form’, or ‘customer details form’ or something similar. Lastly, they should give the customer instructions to tell them what they should do with the form once they have completed it. Here it tells the person fillingtheformin,tosenditbacktotheaddressgiven.

Title: Mr Miss Tick one box Other (Please State Here: )

Travel Arrangement If the information is incorrect, please click the appropriate choice

Bicycle Train Bus Walks Car Coach Taxi Other Route

Dietary Needs

Meal Arrangement If the information is incorrect, please click the appropriate choice

Free school meal Paid school meal Sandwiches Home Other

Fig.7.5Formfilledbythecustomer

Where possible, it is a good idea to try to limit the options that people can enter. If you can manage to do this, then you can set up your computerised system with a drop down box that gives all of the options on the form – making itfasterforstafftoenterthedata.ForExample:Thefirstformshownabove,limitsthechoiceoftitleto‘Mr’or‘Miss’.Thisissufficientinthiscasebecauseitisanapplicationformforachildrens’youthclub,soitisunlikelythat there will be any ‘Mrs’ or ‘Dr’ or ‘Reverend’

The second form gives people the different options for travel; they have to tick one of the options since there isn’t any room for them to write something different. The same method has been used for types of lunches.

7.9VerificationIt was mentioned that validation cannot make sure that data you enter is correct, it can only check that it is sensible, reasonable and allowable. However, it is important that the data in your database is as accurate as possible. Have you ever heard of the term ‘Garbage in, garbage out’ or ‘GIGO’? This means that if you enter data that is full of mistakes (garbage in) then when you want to search for a record you will get data with mistakes presented to you (garbage out).

ThisiswhereVerificationcanhelptomakesurethatthedatainyourdatabasecontainsasfewmistakesaspossible.Verificationmeanstochecksomethingtwice.Thinkaboutwhenyouchooseanewpassword,youhavetotypeitintwice. This lets the computer check if you have typed it exactly the same both times and not made a mistake. The datainyourdatabasecanbeverifiedorcheckedtwice.

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FRUIT COLOUR SIZEApple Yellow MediumOrange Orange MediumStrawberry Red SmallBanana Yellow MediumCherry Red SmallGrape Green SmallMelon Yellow LargeBlacberry Black Small

This can be done in different ways:Somebody else can check the data on the screen for you against the original paper documents.•Youcouldprintoutyourtableandcheckitagainsttheoriginalpaperdocuments.•Youcouldtypeinthedatatwice(likeyoudowithyourpassword),andgetthecomputertocheckthatbothsets•of data are identical.

Othermethodsofverificationincludecontrol,batchorhashtotals.Tofindoutmoreaboutthese,visitthemini-websiteonValidationandVerification.

7.9.1 Editing and CheckingAs well as choosing the correct data types to try to reduce the number of errors made when entering data into the database, there is another method that can be used when setting up the table. This is called ‘Validation’. It is very important to remember that Validation cannot stop the wrong data being entered, you can still enter ‘Smiht’ instead of ‘Smith’ or ‘Brown’ instead of ‘Green’ or ‘78’ instead of ‘87’.

What Validation can do, is to check that the data is sensible, reasonable and allowable. This page will not go into any great depth about different methods of validation as there is a whole mini-website on Validation alone. Go and havealookatittofindoutmoredetailsaboutthebestkindofValidationtouseandthereasonswhy.Someofthetypes of Validation that you could set up for your database are:

Validation Example

Type CheckIf the datatype number has been chosen, then only that type of data will be allowed to be entered i.e. numbers.Ifafieldistoacceptcertainchoicese.g.titlemightbe restricted to ‘Mr’, ‘Mrs’, ‘Miss’ and ‘Ms’ then ‘Dr’ wouldn’t be allowed.

2, 3, 4Mr, Mrs, Miss, MsBrown,Green,Blue,Yellow,Red


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Range CheckA shop may only sell items between the price of ₤ 10.00 and ₤ 50.00 . To stop mistakes being made, a range check can be set up to stop ₤500.00beingentered by accident.

A social club may not want people below the age of 18 to be able to join.

Notice the use of maths symbols:>‘greater than’< ‘less than’= ‘equals’

>=10 AND <=50

>=18

Presence CheckThere might be an important piece of data that you want to make sure is always stored. For example, a school will always want to know an emergency contact number, a video rental store might always want to know a customer’s address, a wedding dress shop might always want a record of the brides wedding date.

Apresencecheckmakessurethatacriticalfieldcannotbeleftblank,itmustbefilledin.

School Database: Emergency contact number DVLA Database: Date test passedElectoral Database: Date of birthVet’s Database: Type of Pet

Picture or format checkSome things are always entered in the same format. Think about postcode, it always has a letter, letter, number, number, number, letter and letter e.g. CV43 9PB. There may be the odd occasion where it differs slightly e.g. a Birmingham postcode B19 8WR, but the letters and numbers are still in the same order.

A picture or format check can be set up to make sure that you can only put letters where letters should be and numbers where numbers should be.

Postcode: CV43 9PBTelephone Number (01926) 615432

Table 7.5 Types of validation

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SummaryData processing is any computer process that converts data into information.•A single datum is a single measurement from the real world.•Data are any facts, numbers, or text that can be processed by a computer.•Whenever a computer is used it must work its way through three basic stages before any task can be •completed.A program is a set of step-by-step instructions which tells the computer exactly what to do with the input in •order to produce the required output.The input stage of computing is concerned with getting the data needed by the program into the computer.•The most commonly used output devices are the screen, which is also called a monitor or VDU and the •printer.The CPU collects all of the raw data from various input devices (such a keyboard or mouse) and converts it into •useful information by carrying out software instructions.The Immediate Access Store (IAS) holds the data and programs needed at that instant by the Control Unit.•Acomputerfileisapieceofarbitraryinformation,orresourceforstoringinformation,thatisavailabletoa•computer program and is usually based on some kind of durable storage.Informationinacomputerfilecanconsistofsmallerpacketsofinformation(oftencalledrecordsorlines)that•are individually different but share some trait in common.Theprogrammerswhocreatetheprogramsdecidewhatfilesareneeded,howtheyaretobeusedand(often)•their names.Filesonacomputercanbecreated,moved,modified,grown,shrunkanddeleted.•Recordsinanorderedsequentialfilearearranged,inorder,onsomekeyfieldorfields.•Inthecaseofaninsertionorupdate,thenewfilewillcontaintheinsertedorupdatedrecord.•Directaccessfilesallowdirectaccesstoaparticularrecordinthefileusingakeyandthisgreatlyfacilitatesthe•operations of reading, deleting, updating and inserting records.ARelativefilemaybevisualisedasaonedimensiontablestoredondisk,wheretherelativerecordnumberis•the index into the table.Anindexedfilemayhavemultiplekeys.•Mostcomputersorganisefilesintohierarchiesusingfolders,directories,orcatalogs.•Manymodern computer systems providemethods for protecting files against accidental and deliberate•damage.

ReferencesThierauf, J. B. & Niehaus, F. J., 1980. • An introduction to data processing for business, Wiley.Micallef, A. B., 1971. • An introduction to data processing, Cummings Pub. Co.Kumar, V. & Kumar, D., • LESSON 1 INTRODUCTION TO DATA PROCESSING [Pdf] Available at: <http://www.ddegjust.ac.in/studymaterial/pgdca/ms-09.pdf> [Accessed 24 May 2013].2 Data Processing Concept• [Pdf] Available at: <http://download.nos.org/srsec330/330L2.pdf> [Accessed 24 May 2013].An Introduction to Data Visualization & Processing - Uttam Grandhi• [Video online] Available at: <http://www.youtube.com/watch?v=EC-8VxXJER4> [Accessed 24 May 2013].Dr. Garg, N., 2008. • Lecture - 1 Introduction to Data Structures and Algorithms [Video online] Available at: <http://www.youtube.com/watch?v=zWg7U0OEAoE> [Accessed 24 May 2013].


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Recommended ReadingRobichaud, B., Muscat, J. E. & Hall, A., 1977. • Introduction to Data Processing, 2nd ed. Greg Division, McGraw-Hill.Carver, K. D., 1974. • Introduction to data processing, John Wiley & Sons Australia, Limited.Harris, L. M., 1986. • Introduction to data processing: mainframes, minis, and microcomputers, 3rd ed. Wiley.

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Self Assessment___________isdefinedaseitherameaningfulanswertoaqueryorameaningfulstimulusthatcancascade1. into further queries.

Data processing a. Informationb. Datumc. Technologyd.

_________aredefinedasnumbersorcharactersthatrepresentmeasurementsfromtherealworld.2. Dataa. Numbersb. Queriesc. Cellsd.


Operational or transactional data1. NominalA.

Non-operational data2. Data about the data itselfB.

Meta data3. Forecast dataC.

Categorical data4. InventoryD.

1-A, 2-D, 3-C, 4-Ba. 1-B, 2-A, 3-D, 4-Cb. 1-D, 2-C, 3-B, 4-Ac. 1-C, 2-B, 3-A, 4-Dd.

The CPU is a microprocessor - a silicon chip - composed of tiny electrical switches called __________.4. transistorsa. megahertzb. microchipsc. processord.

Which of the following statements is false?5. The higher the number of MHz the faster the computer can process information.a. A common CPU today runs at around 3 GHz or more.b. The Intel Pentium processor and the Athlon are examples of a operating system.c. The speed at which the processor carries out its operations is measured in megahertz (MHz) or Gigahertz d. (GHz).


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A computer ________ is a piece of arbitrary information, or resource for storing information, that is available 6. to a computer program and is usually based on some kind of durable storage.

diska. storageb. digitc. filed.

__________filesallowdirectaccesstoaparticularrecordinthefileusingakeyandthisgreatlyfacilitatesthe7. operations of reading, deleting, updating and inserting records.

Relativefilea. Direct accessb. Sequentialfilec. Indexedfilesd.

___________ may have up to 255 keys, the keys can be alphanumeric and only the primary key must be 8. unique.

Relativefilea. Direct accessb. Sequentialfilec. Indexedfilesd.

Anystringof__________mayormaynotbeawell-formednameforafileoralinkdependinguponthecontext9. of application.

charactersa. numbersb. symbolsc. datad.

Whatallowsinstantaccesstocomputerfiles?10. Magnetic tapea. Recordsb. Hard disksc. Fieldsd.

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Chapter VIII

Internet and Network Security

Aim


explaininternet’sworkflow•

elucidate the different threats, consequences and remedies for network security•

explicate the concept of IP address •

Objectives


explain the role of TCP/IP in internet architecture•

enlist the types of threats to network security•

explain different options for optimum network security•

Learning outcome


identify and list key internet architecture components•

understand possible threats to the network security•

describe types of measures useful for network security maintenance•


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8.1 InternetInternet is the world's largest network. It is a unique collection of networks of different kinds. It is often described as “a network of networks” since all the smaller networks are linked together into one giant network called the Internet.

The use of internet began in 1969 in the U.S. Department of Defence’s Advanced Research Project Agency (ARPA) to provide immediate communication within the department during war. Computers were then installed at U.S. universities with defence related projects. As scholars began to go online, the network changed from military use toscientificuse.

As Arpanet grew, administration of the system became distributed to a number of organisations, including the National Science Foundation (NSF). This shift of responsibility began the transformation of the science oriented Arpanet into the commercially minded and funded internet, which is used by millions today.

8.2 Internet ArchitectureInternet has a set architecture which is the basis of its functioning. We need to understand some basic concepts, and terminologies to understand internet better.

8.2.1 ProtocolArchitecture is based in the very specification of the standardTCP/IP protocol, designed to connect any twonetworks which may be very different in internal hardware, software, and technical design. Once two networks are interconnected, communication with TCP/IP is enabled end-to-end, so that any node on the internet has the ability to communicate with any node irrespective of their location. TCP/IP protocol has been discussed in detail in the earlier chapter.

8.2.2 IP Address Every computer on the internet has a unique numerical address, called an Internet Protocol (IP) address, used to route packets across the Internet. Just as a postal address enables the postal system to send mail to the desired destination from anywhere around the world, the computer's IP address gives the internet routing protocols the unique information they need to route packets of information to the computer from anywhere across the Internet. Ifamachineneedstocontactanotherbyadomainname,itfirstlooksupforthecorrespondingIPaddresswiththedomain name service. The IP address is the geographical descriptor of the virtual world, and the addresses of both sourceanddestinationsystemsarestoredintheheaderofeverypacketthatflowsacrosstheInternet.

8.2.3 Domain Name ServiceThe Domain Name System (DNS), as a whole, consists of a network of servers that map internet domain names to a local IP addresses. The DNS enables domain names to stay constant while the underlying network topology and IPaddresseschange.Thisprovidesstabilityattheapplicationlevelwhileenablingnetworkapplicationstofindandcommunicate with each other using the IP no matter how the underlying physical network changes.

8.2.4 Packet SwitchingThe key idea of packet switching is the division of each communication into individual, equal-sized packets. These packets are then sent individually to their destination through the network, and the entire message is reassembled when all the packets arrive. There are a range of procedures for retransmission of packets that might get lost in the network. On the internet, a typical packet length is about one kilobyte, or a thousand characters. A large message may be divided into thousands of individual packets. The beginning of a packet is called the ‘header’ and it records the following information:

Source: the IP address of the computer sending the packet•Destination: the IP address of the destination computer•Length: the length of the packet in bytes•Number: total number of packets in the complete message•Sequence: the number of this packet in the whole list of packets making up this communication.•

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This data provides the information that an internet router needs to get packets and messages to their destination. For additional reliability, internet packet headers also contain an error correction code, which is a number representing a mathematical combination of the rest of the packet data. If even a single bit of the packet is changed in transmission, then recalculation of the error correction code by a router won't match the code transmitted with the message, and the packet will be discarded and a request made for retransmission.

8.2.5 Internet RoutersInternet routers are specialised computers that interconnect the network by switching communications from one line to another at cross points. When a computer communicates with another on the internet, it addresses each packet with the other computer's IP address and then sends it to the closest internet router. The router then uses a routing algorithm to send the packet across the internet to the destination computer.

8.2.6 BackbonesBackbonesaretypicallyfibreoptictrunklines.Thetrunklinehasmultiplefibreopticcablescombinedtogethertoincrease the capacity. Fibre optic cables are designated OC for optical carrier, such as OC-3, OC-12 or OC-48. An OC-3 line is capable of transmitting 155 Mbps while an OC-48 can transmit 2,488 Mbps (2.488 Gbps). Connecting all the hardware, protocols and technologies, we have the internet serving millions of users. But the security of the data transferred, communications using the internet is a big question which needs to be addressed.

8.3 Network SecurityAgoodfirmmayfacepotentialthreatsthroughinternetornetworkingandtheprotectivemeasuresareessentialforsecuring modern business network and IT infrastructure. Although the knowledge of threats and protective methods will not stop all attempts at network incursion or system attack, it can empower to eliminate certain general problems, greatly reducing the potential damages, and quickly detect breaches. With the ever-increasing number and complexity of attacks, vigilant approaches to security in both large and small enterprises are a must.

8.3.1 Understanding Potential ThreatsThreats can come from both internal and external sources. They may be human based, automated or even non intentional natural phenomenon. Their consequences differ as per the type of virus, type of attack, etc. We will have a brief view of the threats and consequences.

Threats Internal/External Consequences

e-mail with virus(viruses are explained after the table)

External origination, internal use

Could infect system reading email and subsequently spread throughout entire organisation.

Network with virus External Could enter through unprotected ports, compromise whole network.

Web based virus Internal browsing to external site

Could cause compromise on system doing browsing and subsequently affect other internal systems.

Web server attack External to web servers

If web server is compromised hacker could gain access to other systems internal to network.

Denial of service attack External Externalservicessuchasweb,emailandfiletransferprotocol could become unusable

If router is attacked, whole network could go down.

Network user attack Internal to anywhere Firewalls do nothing for this attack. Internal segmentation firewallscanhelpcontaindamage.

Table 8.1 Types of threats and consequences.(Source: http://www.ptsdcs.com/whitepapers/70.pdf)


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Viruses A computer virus is a self-replicating computer program that behaves like a biological virus. It spreads by •inserting copies into other executable code or documents. Similar to the biological virus, it spreads on its own by multiplying itself throughout the system. There are •different types of viruses, prominent being Trojan horses, worms, and email viruses. The Trojan horses are computer programs which pretend to do one thing but actually do damage when they •start it. Thewormsvirusesarepiecesofsoftwarethatusecomputernetworksandsecurityflawstocreatecopiesof•self.Acopyofthewormwillthenscanthenetworkforanyothermachinethathasaspecificsecurityflaw,andthen replicate itself to the new machine.With regards to email viruses, these use email messages, and usually will copy and automatically mail itself to •hundreds of people.

8.3.2 Steps towards SecurityAntivirus Software

Antivirus software scans your PC for signatures of a virus. A virus signature is the unique part of that virus. It •canbeafilename,howthevirusbehavesorthesizeofthevirusfileitself.Goodantivirussoftwarewillfindvirusesthathaven'tyetinfectedPCandeliminatetheonesthathavealready•attacked. Antivirussoftwarecanonlyprotectyourcomputerfromvirusestryingtoinfectviaemail,CD-Rom,floppy•disk,Worddocumentsorothertypesofcomputerfiles.Antivirussoftwarealonewillnotkeepcomputer100%safeandusefirewallsoftwareisalsonecessary.

FirewallsAfirewallisamechanismbywhichacontrolledbarrierisusedtocontrolnetworktrafficintoandoutofan•organisational intranet. Firewallsarebasicallyapplicationspecificrouters.Theyrunondedicatedembeddedsystemssuchasaninternet•appliance or they can be software programs running on a general server platform. In most cases these systems will have two network interfaces, one for the external network such as the internet •andonefortheinternalintranetside.Thefirewallprocesscantightlycontrolwhatisallowedtotraversefromone side to the other. Firewalls can range from being fairly simple to very complex. As with most aspects of security, deciding what •typeoffirewall tousewill dependupon factors suchas traffic levels, servicesneedingprotectionand thecomplexityofrulesrequired.Thegreaterthenumberofservicesthatmustbeabletotraversethefirewallthemore complex the requirement becomes.Thedifficultyforfirewallsisdistinguishingbetweenlegitimateandillegitimatetraffic.Evenprivatenetworksare•insecure due to the increased attacks and threats to the networks such as worms, viruses and clever hackers. Securing all equipment, including physical infrastructure equipment such as UPS systems etc, is essential for •a smooth and consistent access to services.

The following list is a set of options that could be used in network security:Firewalls at all public-private network transit points•Versioncontrolledandcentrallydeployedfirewallrulesets•Externalresourcesplacedindualfirewall,dmzprotectednetworks•All network hosts lock down unneeded network ports and turn off unneeded services•All network hosts include centrally managed anti-virus software and utilise central security updates•Secure central authentication such as radius, windows/kerberos/active directory•

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Centrally managed user management with password policy (must change every three months and must be a •‘secure password’)Proactive network scanning for new hosts, out of date systems•Network monitoring for suspicious behaviour•Incident response mechanisms (policies, manual, automated and so on).•

8.4 Uses of InternetIn spite of all the security issues discussed above, networks, especially internet, are one of the most essential componentsofroutinelifeofindividuals.Thisisnottoexaggerate,buttounderlinethesignificanceofinternetandits services in today’s world.

Some of the important applications of internet are:Access to remote information•World wide web•Person-to-person communication with electronic mail, videoconference, and so on•Interactive entertainment like video-on-demand, games and so on•Online shopping, booking, trading, social networking and so on.•


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SummaryThe use of internet began in 1969 at the U.S. Department of Defence’s Advanced Research Project Agency •(ARPA) to provide immediate communication within the department in case of war.The key components of internet architecture are the protocol, IP address, domain name service, packet switching, •internet routers, and backbone.SecuringthemodernbusinessnetworkandITinfrastructuredemandsanend-to-endapproachforfirmsingraspof•possible security threats and should be associated with protective measures. Threats can come from both internal and external sources. They may be human based, automated or even non intentional natural phenomenon.A computer virus is a self-replicating computer program that behaves like a biological virus. There are different •types of viruses like Trojan horses, worms, and email viruses.Securingallequipment,includingphysicalinfrastructureequipmentisessential.Antivirussoftware,firewalls,•etc. can be used as measures for secure network usage.Internet has enhanced and eased access to remote information and communication, with some of its services •like the World Wide Web.

ReferencesOppliger, R., 2001. • Internet and Intranet security, 2nd ed. Artech House.Kizza, M. J., 2005.• Computer Network Security, Springer.Dr.JamesH.Yu&Mr.TomK.Le,• Internet and Network Security [Pdf] Available at: <http://www.nait.org/jit/Articles/yu101800.pdf> [Accessed 28 May 2013].Network Security: History, Importance, and Future• [Pdf] Available at: <http://web.mit.edu/~bdaya/www/Network%20Security.pdf> [Accessed 28 May 2013].Prof. Ghosh, S., • Lecture - 38 Security [Video online] Available at: <http://www.youtube.com/watch?v=3JblSrRT8XE> [Accessed 28 May 2013].Prof. Sengupta, I., 2008. • Lecture - 31 Intranet, Extranet, Firewall [Video online] Available at: <http://www.youtube.com/watch?v=vS0khTah3zU> [Accessed 28 May 2013].

Recommended Reading McNab, C., 2009. • Network Security Assessment: Know Your Network, 2nd ed. O'Reilly Media, Inc.Joshi, J., 2008. • Network Security: Know It All: Know It All, Morgan Kaufmann.Maximum Security• , 4th ed. Sams Publishing

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Self AssessmentSince all smaller networks are linked together into one giant network called the internet, it is also known as 1. ____________.

internet networksa. network of networksb. large networkc. linked networkd.

Internet began under which U.S. department?2. National Defence Agencya. National Science Foundationb. Advanced Research Project Agencyc. Advanced Defence Project.d.

Two networks which may be very different in internal hardware, software, and technical design are connected 3. with the help of?

TCP/IP protocola. Cablesb. Connectorsc. Communicatorsd.

An Internet Protocol (IP) address is used to ____________across the internet. 4. packet switchinga. route switchingb. address locationc. route packetsd.

The key idea of packet switching is the division of each communication into individual ____________.5. large packetsa. small packetsb. equal-sized packetsc. uneven packetsd.

Which of the following information is not recorded by the packet header?6. Destinationa. Dateb. Lengthc. Sequenced.

Router uses ____________ to send the packet across the internet to the destination computer.7. route switchinga. routing messageb. packet switchingc. routing algorithmd.


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The____________hasmultiplefibreopticcables.8. trunk linea. hardwareb. connectorsc. switchesd.

Trojan horse is a type of:9. Computer soft warea. Computer virusb. Computer hard warec. Security systemd.

Firewallsarebasicallyapplicationspecific____________.10. systemsa. hurdlesb. routersc. protocolsd.

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Application I

Computers in Airline Reservations

A computer reservation system or CRS is a computerised system that is used for reservation purpose in airlines, railways and buses. This computerised system is used to store and retrieve information; and conduct transactions related to the transport. This was originally designed and operated by airlines.

Thus, computer technology has made the airline reservation system quite effective and less time consuming. It is observed that reservation system in airlines is almost error free and provide various facilities.

A typical airline system includes following information:Flight details: This includes the information like starting destination and end destination, along with the stops •in between, and the number of seats booked/available.Customer description: This section includes customer’s name, code, address, phone number, and seat number •allotted. This information is useful for keeping the records of customers for any emergency.Reservationdescription:Thisincludesinformationlikecustomer’scodenumber,flightnumber,dateofbooking,•and date of travelling.

The computerised reservation system has made the reservation procedure of airlines easier and less time-consuming. The airlines are able to meet their ticket sales target and maintain their tickets selling ratio. It also reduces confusion from the point of view of customers. Thus, computer technology has transformed the reservation system in the airline industry and relieved the customers from a tedious and prolonged reservation procedure.

QuestionsHow is the computer technology useful in the airline reservation?1. AnswerThe computerised reservation system or CRS is used in the airline reservation. This form of computer technology is used to store and retrieve information; and conduct transactions related to the transport.

What are the advantages of computerised reservation system for the airline industry?2. AnswerThe advantages of the computerised reservation system for the airline industry are as follows:

The computerised reservation system has made the airline reservation system quit effective and less time-•consuming.It is observed that reservation system in airlines is almost error free and provide various facilities. •Due to CSR, the airlines are able to meet their ticket sales target and maintain their tickets selling ratio. •It has also reduced confusion from the point of view of customers and have made travelling a lot more •easier.

What information is available on a typical airline system?3. AnswerA typical Airline System includes following information:

Flight details: It includes the information like starting destination and end destination, along with the stops •in between, and the number of seats booked/available.Customer description: This section includes customer’s name, code, address, phone number, and seat number •allotted. This information is useful for keeping the records of customers for any emergency.Reservationdescription:Itincludesinformationlikecustomer’scodenumber,flightnumber,dateofbooking,•and date of travelling.


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Howisthecomputerisedreservationsystembeneficialfromthepointofviewofcustomers?4. AnswerThe computerised reservation system has made the reservation procedure of airlines easier and less time-consuming. It has reduced the confusion from the point of view of customers. Thus, it has relieved the customers from a tedious and prolonged reservation procedure. It has eased the payment procedure and has made travelling a simple procedure.

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Application II

Computers in Education and Training

Computers have transformed the traditional form of teaching and training. The advent of computers has made a remarkable change in children’s life. It has enhanced their knowledge and has given a wider scope to search information they need.

Computers serveasa tool ineducationand trainingfield. It canbeusedasdifferent typeof tool fordifferentpurposes:Communications Tool

e-mail•cell phones•

Publishing Toolpresentation software•drawing software•internet publication•reports•

Research Toolinternet access•library card catalogue•periodical listing•reference software•

Teaching Tooldrill and practice•interactive instruction•modelling•programming•tutorials•

Advantages of Computers in EducationComputers help the school children to be in control of their experience, set their own pace, and to select the •level of challenge which they feel comfortable. To extract the information, the children make use of all their senses and there is no spoon feeding from their •mentors. Thus, children gain information in less time. Computers fascinate the kids and draw their attention, making them more attentive and help in concentrating.•Computers also help in enhancing creative skills like painting, making up stories, solving puzzles and so •forth.Good educational software can make the learning to be a cheerful experience and full of activities for the children. •This reduces the work of teachers and gives them better opportunities in developing the teaching skills.Good educational software enables children to develop and practice many skills like letters, numbers, shapes, •colours, rhythm and the likes.


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Thus,computershavemadearemarkablechangeineducationfieldbyimplementinggoodeducationalsoftwares.This makes teaching easier for the teachers and facilitates quick learning for children.

QuestionsExplain the role of computers as a teaching tool?1. How has the training and education transformed after the introduction of computers?2. What are the advantages of computers in educating school children?3. How can good educational software reduce the work of teachers?4.

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Application III

Computers in Banking

Today’s computer technology has transformed the traditional banking system with the online banking concept. The online banking is one of the forms that have helped the banks and the customers in various ways. The online banking is less time –consuming, and has reduced the work of the people. Thus, it has reduced the work of the banks and made the transaction of money easier.

Origin of Online BankingThe introduction of internet and the popularity of personal computers, both gave an opportunity and challenge for the banking industry. The concept of online banking slowly began to spread in most of the banks as it reduced a lot of burden of work of both the bank and the customer. After the online banking concept was established, many banks faced problems in initial stages of setting the online system. However, slowly, online banking became popular and was powerful “value added tool” to attract and retain customers. It also helped to eliminate the lengthy banking transactionprocedures,costlypaperhandlingandtellerinteractions,andmadebankstostandfirmincompetitivebanking environment. Since people are now aware of the online banking concept and are familiar in handling it, banks have developed stable online banking and offer variety of services online.

The computer technology has helped banking sector to set up different types of banking facilities like:PC banking•home banking•electronic banking•internet banking.•

AdvantagesThe advantages of online banking are as follows:

Convenience: Online banking facilities are available 24 hours, seven days a week, unlike the normal banks. Thus, •online banking is quite convenient. It can be accessed even if a customer is in other country or other state. Transaction speed: Online banking sites execute the transactions quicker than the ATM processing.•Efficiency:Onlinebankingissecuredandonecaneasilyaccessandmanagethebankaccounts,whichinclude•IRA’s, CD’s and so on.Effectiveness: Most of the online banking sites offer different tools like account aggregation, stock quotes, •rate alerts andportfoliomanagingprograms, transfers and soon that arebeneficial inmanagingall assetseffectively.

DisadvantagesThere are also some disadvantages of online banking. These are as follows:

Longer Start-up phase: In order to register with the online banking, the bank should provide ID and this may •taketime.Thebanksitesmaytakelongertimewhiletryingtoregisterforthefirsttime.Learning curve: Banking sites may be confusing to some people and they may end up processing incorrect •transactions. Bank site changes: Most of the banks may incorporate changes in the bank sites or upgrade the sites and this •may create problems for the customers.LackofTrust:Mostofthepeoplefinditdifficulttotrustthebanksites.Oldpeoplemayfinditdifficulttotrust•the security of the transactions online and prefer the banking transaction to be carried out personally. Also, people fear the incidents of online account hacking.


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Mostofthepeoplefindonlinebankingasaflexiblemodeofmoneytransaction,andtheycanviewtheiraccountsat a click. Thus, computer technologies have changed the life of customers and also have transformed the way banking sector used to work.

QuestionsHow has computer technology transformed the traditional banking concept?1. What are the advantages and disadvantages of online banking?2. Which are the different ways in which computer technology is used in banking sector?3. How is online banking convenient than the traditional form of banking?4.

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Kesidis, G., 2007. • An Introduction to Communication Network Analysis, John Wiley & Sons.Kifer, M. & Smolka, S., 2007. • Introduction to Operating System Design and Implementation: The OSP 2 Approach, Springer.Kizza, M. J., 2005.• Computer Network Security, Springer.Kumar, V. & Kumar, D., • LESSON 1 INTRODUCTION TO DATA PROCESSING [Pdf] Available at: <http://www.ddegjust.ac.in/studymaterial/pgdca/ms-09.pdf> [Accessed 24 May 2013].Learn Introduction to O S from the Fundamentals of Operating Systems• [Video online] Available at: <http://www.youtube.com/watch?v=cP-OPjwag4E> [Accessed 22 May 2013].Lecture - 3 Introduction To System : Hardware [Video online] Available at: <http://www.youtube.com/•watch?v=FOyuMclwymw> [Accessed 28 May 2013]Logic gates• [Pdf] Available at: <http://education.cambridge.org/media/577240/cambridge_igcse_computer_studies__revision_guide___cambridge_education___cambridge_university_press_samples.pdf> [Accessed 29 May 2013].Logic Gates• [Pdf] Available at: <http://ptgmedia.pearsoncmg.com/images/chap3_0130619701/elementLinks/chap3_0130619701.pdf> [Accessed 29 May 2013].Meena, K., 2009. • Principles of Digital Electronics, PHI Learning Pvt. Ltd.Micallef, A. B., 1971. • An introduction to data processing, Cummings Pub. Co.Murphy, M., 2011. • Introduction to Operating Systems [Video online] Available at: <http://www.youtube.com/watch?v=MzVGL44eq9w> [Accessed 22 May 2013].Network Security: History, Importance, and Future• [Pdf] Available at: <http://web.mit.edu/~bdaya/www/Network%20Security.pdf> [Accessed 28 May 2013].Number Systems and Codes• [Pdf] Available at: <http://www.inf.fu-berlin.de/lehre/WS00/19504-V/Chapter1.pdf> [Accessed 19 June 2013]Number Systems, Base Conversions, and Computer Data Representation• [Pdf] Available at: <http://www.eecs.wsu.edu/~ee314/handouts/numsys.pdf> [Accessed 19 June 2013]Oppliger, R., 2001. • Internet and Intranet security, 2nd ed. Artech House.Prof. Ghosh, S., • Lecture - 38 Security [Video online] Available at: <http://www.youtube.com/watch?v=3JblSrRT8XE> [Accessed 28 May 2013].Prof. Ghosh, S., L• ecture -1 Emergence of Networks & Reference Models [Video online] Available at: <http://www.youtube.com/watch?v=3DZLItfbqtQ&list=PLD6F332057F76C54C> [Accessed 28 May 2013].Prof. Kumar, A., 208. • Lecture -1 Introduction to Computer Architecture [Video online] Available at: <http://www.youtube.com/watch?v=4TzMyXmzL8M> [Accessed 28 May 2013].Prof. Sengupta, I., 2008. • Lecture - 31 Intranet, Extranet, Firewall [Video online] Available at: <http://www.youtube.com/watch?v=vS0khTah3zU> [Accessed 28 May 2013].Protocols and Computer Networks part 1• [Video online] Available at: <http://www.youtube.com/watch?v=Q3SsVO0eSOU> [Accessed 28 May 2013]Rafiquzzaman,M.,2005.• Fundamentals of Digital Logic and Microcomputer Design, 5th ed., John Wiley & Sons.Shelly, B. G. & Vermaat, E. M., 2009. • Discovering Computers: Living in a Digital World : Fundamentals, 6th ed. Cengage Learning.Shim, K. J., 2002. • Information Systems and Technology for the Noninformation Systems Executive: An Integrated Resource Management Guide for the 21st Century, CRC Press.Stallings, W., 2007. • Data And Computer Communications, 8/E, 8th ed. Pearson Education India.Thierauf, J. B. & Niehaus, F. J., 1980. • An introduction to data processing for business, Wiley.

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Recommended ReadingBagad, V.S. & Dhotre, I. A., 2009. • Computer Communication Networks, Technical Publications.Bhatt, 2007. • Introduction To Operating Systems: Concepts And Practice An 2Nd Ed., 2nd ed. PHI Learning Pvt. Ltd.Carver, K. D., 1974. • Introduction to data processing, John Wiley & Sons Australia, Limited.Godse, A. P. & Godse, D. A., 2009. • Digital Electronics and Logic Design, Technical Publications.Godse, A.P. & Godse, D.A., 2005. • Digital Systems, Technical Publications.Godse, A.P. & Godse, D.A., 2008. • Digital Logic and Design and Application, Technical Publications.Harris, L. M., 1986. • Introduction to data processing: mainframes, minis, and microcomputers, 3rd ed. Wiley.Jaeger, T., 2008. • Operating Systems Security, Morgan & Claypool Publishers.Johnson, P., 2004. • Introduction To Operating Systems, iUniverse.Joshi, J., 2008. • Network Security: Know It All: Know It All, Morgan Kaufmann.Kasera, S. & Narang, N., 2005. • Communication Networks: Principles and Practice, Tata McGraw-Hill Education.Maximum Security• , 4th ed. Sams Publishing.McNab, C., 2009. • Network Security Assessment: Know Your Network, 2nd ed. O’Reilly Media, Inc.Mir, F. N., 2006.• Computer and Communication Networks, Pearson EducationP. Norton, 2002. • Introduction To Computers (Sie), Tata McGraw-Hill Education.Preez, D. A., Dyk, V. V. & Cook, A., 2008. • FCS Computer Hardware & Software L3, Pearson South AfricaRobichaud, B., Muscat, J. E. & Hall, A., 1977. • Introduction to Data Processing, 2nd ed. Greg Division, McGraw-Hill.Saha, A. & Manna, N., 2009. • Digital Principles and Logic Design Engineering series, Jones & Bartlett Learning.Schneidewind, F. N., 2012. • Computer, Network, Software, and Hardware Engineering with Applications, John Wiley & Sons.Shelly, B. G. & Vermaat, E. M., 2008. • Discovering Computers 2009, Cengage Learning.Shelly, B. G. & Vermaat, E. M., 2011. • Discovering Computers, Brief: Your Interactive Guide to the Digital World, Cengage Learning.Sichel, E. D., 1997. • The computer revolution: an economic perspective, Brookings Institution Press.Tokheim, 2004. • Digital Electronics Principles and Applications, Tata McGraw-Hill Education.


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Self Assessment Answers

Chapter Ia1. b2. c3. d4. a5. b6. c7. d8. a9. b10.

Chapter IId1. b2. c3. a4. d5. b6. c7. a8. d9. c10.

Chapter IIIb1. a2. c3. d4. b5. c6. d7. a8. c9. b10.

Chapter IVb1. a2. c3. d4. b5. a6. d7. a8. b9. c10.

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Chapter Vc1. b2. a3. d4. a5. b6. c7. d8. b9. a10.

Chapter VIa1. b2. d3. b4. c5. b6. c7. d8. c9. a10.

Chapter VIIc1. b2. a3. d4. a5. b6. c7. d8. b9. a10.

Chapter VIIIb1. c2. a3. d4. c5. b6. d7. a8. b9. c10.

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