;1. 1 What is a computer?

An electronic machine, operating under the control of instructions stored in its own memory

• accepts data• manipulates the data according to

specified rules• produces results• stores the results for future use

1.2 Early computer development

1.2.1 The Abacus

Even before humans could read or write, they needed to count. First they used their fingers, but when they had to deal with figures over ten, a counting device became necessary. Pebbles and bits of wood arranged on the ground were used to count goods and to figure prices. These were the predecessors of the abacus. The

abacus has two distinct variations: the counting board and the bead frame abacus. The Abacus dates back at least to 1100 BC and is still in use today, particularly in Asia.

The bead frame abacus as we know it today was probably invented by the Chinese sometime around the second century AD. It is usually made of a wooden frame with 13 vertical wires and 7 beads on each wire. The Japanese adopted and modified the Chinese abacus around the 17th century, reducing the number of beads on each wire to six and later on to five. A third form of the abacus is the Russian abacus which was probably brought to Russia from China and was modified for counting in rubles.

1.2.2 Tha Pascaline

With the need to deal with higher and higher figures, a more sophisticated counting machine became necessary,

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but little progress was made beyond the abacus until the beginning of the seventeenth century, whose great minds gave birth to the first ideas concerning mechanical computation.

The first counting device - a mechanical “Calculating Clock” was invented byWilhelm Schickard in 1624, but was forgotten for a time, so the man usuallycredited with inventing the first mechanical calculator is Blaise Pascal, between 1642 and 1644. Pascal, a French scientist and inventor, created a device in 1642 which, unlike the passive abacus, performed mathematical operations in an active manner. This calculator, called the ‘Pascaline’, could add and subtract numbers with up to eight digits, but was never used much because of its high cost and unreliability. It could only do addition and subtraction, with numbers being entered by manipulating its dials. Pascal invented the machine for his father, a tax collector, so it was the first business machine, too (if one does not count the abacus). He built 50 of them over the next 10 years.

1.2.3 Tha Leibnitz Machine

In 1671 the German mathematician-philosopher Gottfried Wilhelm von Leibniz designed a calculating machine called the Step Reckoner. (It was first built in 1673. See

photograph.) The Step Reckoner expanded on Pascal's ideas and did multiplication by repeated addition and shifting.Leibniz was a strong advocate of the binary system. Binary numbers are ideal for machines because they require only two digits, which can easily be represented by the on and off states of a switch. When computers became electronic, the binary system was particularly appropriate because an electrical circuit is either on or off. This meant that on could represent true, off could represent false, and the flow of current would directly represent the flow of logic. Leibniz was prescient in seeing the appropriateness of the binary system in calculating machines, but his machine did not use it. Instead, the Step Reckoner represented numbers in decimal form, as positions on 10-position dials.

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1.2.4 The Babbage Machine

Charles Babbage, a professor of mathematics, developed a machine called Difference Engine in the year machine was expected to calculate logarithm tables to a high degree of precision. The difference engine was made to calculate various mathematical functions. The machine was capable of polynomial evaluation by finite difference and its operation was automatic multistop operation.

Babbage’s Analytical Engine.The Analytical Engine was to be a general-purpose, fully program-controlled, automatic mechanical digital computer. It would be able to perform any calculation set before it. Before Babbage there is no evidence that anyone had ever conceived of such a device, let alone attempted to build one. The machine was designed to consist of

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four components: the mill, the store, the reader, and the printer. These components are the essential components of every computer today. The mill was the calculating unit, analogous to the central processing unit (CPU) in a modern computer; the store was where data were held prior to

processing, exactly analogous to memory and storage in today's computers; and the reader and printer were the input and output devices.

1.3 Generations of Computers

The history of computer development is often referred to in reference to the different generations of computing devices. Each generation of computer is characterized by a major technological development that fundamentally changed the way computers operate, resulting in increasingly smaller, cheaper, more powerful and more efficient and reliable devices.

1.3.1 First Generation Computers

First Generation (1940-1956) Vacuum Tubes The first computers used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms. They were very expensive to operate and in addition to using a great deal of electricity, generated a lot of heat, which was often the cause of malfunctions.

First generation computers relied on machine language, the lowest-level programming language understood by computers, to perform operations, and they could only solve one problem at a time. Input was based on punched cards and paper tape, and output was displayed on printouts.

The UNIVAC and ENIAC computers are examples of first-generation computing devices. The UNIVAC was the first commercial computer delivered to a business client, the U.S. Census Bureau in 1951.

1.3.2 Second Generation Computers

Second Generation (1956-1963) Transistors Transistors replaced vacuum tubes and ushered in the second generation of computers. The transistor was invented in 1947 but

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did not see widespread use in computers until the late 1950s. The transistor was far superior to the vacuum tube, allowing computers to become smaller, faster, cheaper, more energy-efficient and more reliable than their first-generation predecessors. Though the transistor still generated a great deal of heat that subjected the computer to damage, it was a vast improvement over the vacuum tube. Second-generation computers still relied on punched cards for input and printouts for output.

Second-generation computers moved from cryptic binary machine language to symbolic, or assembly, languages, which allowed programmers to specify instructions in words. High-level programming languages were also being developed at this time, such as early versions of COBOL and FORTRAN. These were also the first computers that stored their instructions in their memory, which moved from a magnetic drum to magnetic core technology.

The first computers of this generation were developed for the atomic energy industry.

1.3.3 Third Generation Computers

Third Generation (1964-1971) Integrated Circuits. The development of the integrated circuit was the hallmark of the third generation of computers. Transistors were miniaturized and placed on silicon chips, called semiconductors, which drastically increased the speed and efficiency of computers.

Instead of punched cards and printouts, users interacted with third generation computers through keyboards and monitors and interfaced with an operating system, which allowed the device to run many different applications at one time with a central program that monitored the memory. Computers for the first time became accessible to a mass audience because they were smaller and cheaper than their predecessors.

1.3.4 Fourth Generation Computers

Fourth Generation (1971-Present) Microprocessors. The microprocessor brought the fourth generation of computers, as thousands of integrated circuits were built onto a single silicon chip. What in the first generation filled an entire room could now fit in the palm of the hand. The Intel 4004 chip, developed in 1971, located all the components of the computer—from the central processing unit and memory to input/output controls—on a single chip.

In 1981 IBM introduced its first computer for the home user, and in 1984 Apple introduced the Macintosh. Microprocessors also moved out of the realm of desktop computers and into many areas of life as more and more everyday products began to use microprocessors.

As these small computers became more powerful, they could be linked together to form networks, which eventually led to the development of the Internet. Fourth generation computers also saw the development of GUIs, the mouse and handheld devices.

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1.3.5 Fifth Generation Computers

Fifth Generation (Present and Beyond) Artificial Intelligence. Fifth generation computing devices, based on artificial intelligence, are still in development, though there are some applications, such as voice recognition, that are being used today. The use of parallel processing and superconductors is helping to make artificial intelligence a reality. Quantum computation and molecular and nanotechnology will radically change the face of computers in years to come. The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and self-organization.

1.4 Types of Computers

There are four different types of computers when we classify them based on their performance and capacity. The four types are

1. Super Computers2. Mainframe Computers3. Mini Computers4. Micro Computers

1.1.4 Super Computers

When we talk about types of computers, the first type that comes to our mind would be Super computers. They are the best in terms of processing capacity and also the most expensive ones. These computers can process billions of instructions per second. Normally, they will be used for applications which require intensive numerical computations such as stock analysis, weather forecasting etc. Other uses of

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supercomputers are scientific simulations, (animated) graphics, fluid dynamic calculations, nuclear energy research, electronic design, and analysis of geological data (e.g. in petrochemical prospecting). Perhaps the best known super computer manufacturer is Cray Research. Some of the "traditional" companies which produce super computers are Cray, IBM and Hewlett-Packard.

As of July 2009, the IBM Roadrunner, located at Los Alamos National Laboratory, is the fastest super computer in the world.

If you want to know more advanced details about super computers, refer to SuperComputers

1.4.3 Mainframe Computers

Mainframe computers can also process data at very high speeds vi.e., hundreds of million instructions per second and they are also quite expensive. Normally, they are used in banking, airlines and railways etc for their applications.

1.4.2. Mini Computers

Mini computers are lower to mainframe computers in terms of speed and storage capacity. They are also less expensive than mainframe computers. Some of the features of mainframes will not be available in mini computers. Hence, their performance also will be less than that of mainframes.

1.4.1 Micro Computers

The invention of microprocessor (single chip CPU) gave birth to the much cheaper micro computers. They are further classified into

1. Desktop Computers2. Laptop Computers3. Handheld Computers (PDAs)

Desktop Computers

Today the Desktop computers are the most popular computer systems.These desktop computers are also known as personal computers or simply PCs. They are usually easier to use and more affordable. They are normally intended for individual users for their word processing and other small application requirements.

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Laptop Computers

Laptop computers are portable computers. They are lightweight computers with a thin screen. They are also called as notebook computers because of their small size. They can operate on batteries and hence are very popular with travellers. The screen folds down onto the keyboard when not in use.

Handheld Computers

Handheld computers or Personal Digital Assistants (PDAs) are pen-based and also battery-powered. They are small and can be carried anywhere. They use a pen like stylus and accept handwritten input directly on the screen. They are not as powerful as desktops or laptops but they are used for scheduling appointments, storing addresses and playing games. They have touch screens which we use with a finger or a stylus.

Unit 2 Hardware : Components of Computer System

Hardware: The electric, electronic, and mechanical equipment that makes up a computer

Computer System A complete, working computer. The computer system includes not only the computer, but also any software and peripheral devices that are necessary to make the computer function. Every computer system, for example, requires an operating system.

To perform its function, the computer must have some means of:Function Associated Hardware

Processing data - Processor - (Central Processing Unit - (CPU)) Accepting data - Input Device Storing data - Memory Devices – Primary and Secondary Memory Outputting data - Output Device

These hardware components are referred to as the general components of a computer system. Sometimes, input and output functions are combined in one device. In these cases, the combined unit is referred to as an Input/Output or I/O device.

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2.1 Parts of a Computer

2.2 Input devices

2.2.1 What is input? Any data or instructions you enter into the memory of the computer Users can input data and instructions in a variety of ways

What are two types of input?

Human readable data is data that can be read by a human, like text and drawings, but not magnetic patters

Machine readable data is data that can be input to a computer using a suitable input device without the need for any preparation

- Data - A collection of raw unprocessed facts, figures, and symbols- Instructions

• Programs• Commands• User responses

2.2.1 What is an input device? Any hardware component that allows you to enter data, programs, commands, and

user responses into a computer

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2.2.2 Types of Input Devices and their uses

Input devices fall into the following categories:

o Keyboard o Pointing devices o Scanners o Reading devices o Digital cameraso Audio and video input deviceso Input devices for physically challenged

The following are examples:Keyboard is an input device with keys like a typewriter. There are keys

for letters, digits, arithmetic operations, punctuation marks, special symbols like &, navigation keys (arrows and Home, PageUp etc.), special keys like Ctrl, function keys (F1-F12), different lock keys, Enter, Delete, Backspace, Spacebar and more. (typically 104)

Key-to disk is keyboard entry of data directly to magnetic disk without previous preparation on another medium.

Scanner is an input device which is passed over the information to be input into the computer. The input may later be edited graphically or in a word processor if OCR software is used.

Optical Mark Reader (OMR)

is an input device that reads marks made in predetermined positions on special forms (or cards) by a light-sensing method. Used to mark multiple-choice papers.

Optical Character Reader (OCR)

is machine recognition of printed characters by light-sensing methods. Used to read typed post codes when mail is automatically sorted.

Magnetic Ink Character is machine recognition of stylised characters printed in

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Reader (MICR) magnetic ink. Used to read the cheque number, the branch number and the account number on bank cheques. These characters are both machine and human readable.

Mouse is an input device that controls the movement of the cursor. The cursor moves in response to the movement of the mouse on a flat surface. The mouse can select objects, drag objects and make menu choices.

Joystick is an input device that uses a lever to control cursor movement or graphic images. Often used in games.

Graphics pad/tablet is a device used to input line drawings into a computer. The user draws with a stylus onto a flat pad or tablet, either copying a drawing or working freehand.

Lightpen is a light-sensitive input device which when it touches the screen detects the presence or absence of light. It is used to select an entry or indicate a position.

Terminal is the combination of a monitor and keyboard to input and check data and to view output. A terminal does not necessarily include a processor.

Touch terminal Also called a touch screen. A device that allows data to be input by touching a screen with the finger or other object. The surface of the screen consists of a number of programmed touch points each of which may trigger a different action when selected by the user.

Point of sale terminal POS

is a device that can scan bar codes and get the cost and item description from a database connected to the network all the POS’s are on.

Bar code is a pattern of parallel black-and-white lines used to represent a code number, which can then be read automatically.

voice data entry VDEspeech recognition

is a process of analysing a spoken word and comparing it with those known to the computer system. Used to give limited set of commands to a computer operated wheel-chair. Also used to read in complete documents into a word processor.

2.3 Output devices

2.2.1 What is output?

An output device is a peripheral device that converts signals from a computer into a human-readable form (usually alphanumeric characters) or into a form suitable for reprocessing (e.g. magnetic patterns on a disk) by the computer.

Output devices may produce information that is temporary (soft copy) or permanent (hard copy). These terms are defined as follows:

hard copy permanent computer output e.g. computer output printed on papersoft copy temporary computer output e.g. computer output on a monitor

Common output devices include:

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Monitor/ Visual Display Unit (VDU)

is a television like device used to display data. The display of the monitor is made up of illuminated dots (called pixels).Terms associated with a monitor’s display are: Pixel (means picture-element) is the smallest amount of the screen that can

be changed by the computer - i.e. a single point in a graphic image. Resolution refers to the sharpness and clarity of an image. It is a measure of

the number of pixels displayed on the screen; e.g. a 640-by-480 pixel screen is capable of displaying 640 distinct dots on each of 480 lines, or about 300,000 pixels. This translates into different dpi measurements depending on the size of the screen. For example, a 15-inch VGA monitor (640x480) displays about 50 dots per inch. The higher the resolution the greater the detail that can be displayed.

Printer a computer peripheral that puts text or a computer generated image on paper or some other medium such as a transparency.Terms associated with printer usage are: Print speed is a description of how many pages can be printed per minute. Print quality is a description of how well-formed the characters are when

printed. e.g. correspondence quality, near letter quality and draft quality. Print resolution is a measure of the number of dots per square inch. e.g. a

300-dpi (dots per inch) printer is one that is capable of printing 300 distinct dots in a line one inch long. This means it can print 90,000 dots per square inch

Printer buffer is a storage area, usually in the printer, which receives the information to be printed and stores it until it is printed.

Printer Types:1. Character printer is one which prints one character at a time.

Examples: daisy wheel printer, dot matrix printer, golf ball printer.2. Line printer is one that prints a complete line of characters at one time.

Examples: barrel printer, chain printer.3. Page printer is one which forms and prints a whole page in one operation.

Example: laser printer.4. Impact printer is one which creates marks on the page by striking an inked ribbon against the

page.

The object that strikes the ribbon may form complete characters at one strike, as in a daisy wheel or golf ball printer, or may form a pattern of dots, as in a dot matrix printer.Dot-matrix printers (which produce characters consisting of dots by hammering pins onto a ribbon), are fast but print quality is poor - useful for multiple-part stationery

5. Thermal printer apply heat to heat-sensitive paper - may be used to print receipts at POS terminals.

6. Ink jet printer is a non-impact printer which produces an image by spraying a fine jet of quick-drying ink onto the paper.

They are cheaper than laser printers but can be expensive to run - the ink cartridges are expensive.

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7. Laser printer is a non-impact printer which uses a laser to ‘write’ the image to be printed onto a light-sensitive drum. Method:

The drum then uses electrostatics (as in a photo copier) to attract toner, a black fine plastic powder, to coat the image with powder. Paper is then pressed against the drum transferring the toner to the paper. The paper is finally heated to melt the toner onto the paper.

A laser printer produces output of high quality, and is virtually silent (a good idea in a busy office) A Laser printer may be combined with a scanner, a photocopier and a fax machine to form one device.

Plotter is an output device which moves one or more pens across paper to produce an output of graphical data. Printing is achieved by the drawing of continuous lines.Architects, surveyors and engineers often use plotters to output their work – maps; charts; engineering drawings.

Computer Output on Microfilm or Microfiche (COM) Device

COM reader

COM is a technique of reducing documents in size and photographically printing them so that they can be read using a special magnifying machine.

Microfiche is an output medium consisting of a rectangular sheet of film on which many frames (pages of information) can be stored. Special microfiche readers with big screens are needed to view the data. (See diagram at left)

The principle advantages of this technology are Speed – can easily handle output at a rate in excess of

30,000 lines per minute. Size – stores a high volume of data per unit area; uses

much less storage space. Cost per unit volume – the cost per page of printed data is

less than that of regular hard copy output methods. Durability - film lasts longer than paper

Libraries and archives use this method to store records and reference materials; also Newspapers might be archived on microfiche.

Voice/speech synthesiser is an output device that generates sound similar to human speech on receipt of digital signals.

Some computer peripherals do double duty as both input and output units. These devices

are collectively referred to as I/O devices and include secondary storage devices such as

hard disk drives, floppy disk drives and magnetic tape drives, as well as communication

devices called modems (modulator/demodulator). Modems enable one computer to

converse with another computer over either standard or dedicated telephone lines.

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2.4 Primary storage devices and media

Primary storage is that part of the computer where instructions and data to be used by the computer, are stored. It is directly accessible by the CPU consists of high-speed semiconductor devices that are compatible with the microprocessor’s speed so as not to significantly slow its operation.

Primary storage consists of two major types:

Read-Only Memory (ROM) – used to hold data in a permanent form. Random Access Memory (RAM) - used for temporary storage of data.

1. ROM Memory

ROM memories generally hold data that was programmed into them at the factory and

are not intended to be changed.

There are several types of ROM, some of which can be erased and reprogrammed (but not during the normal operation of the computer). These classes include the following:

Programmable ROM (PROM) - can be custom-programmed by the user (once) using special circuitry.

Erasable-Programmable ROM (EPROM) - can also be programmed and erased by the user using ultraviolet light and special circuitry external to the computer.

Electrically Erasable PROM (EEPROM) - can be erased and reprogrammed by special circuitry within the computer. i.e. the computer system can be changed through the use of software rater than replacing the ROM.

Note that all forms of ROM are all non-volatile. This means that the data contained in the memory is not lost when the computer is turned off or when electrical power is lost. This enables the computer to begin reading instructions and data from this type of memory as soon as the power is turned on.

ROM Applications

Some common ROM applications are as follows:

Firmware storage - the computer’s operating system programs and language interpreters are stored in ROM devices so that the computer can begin operation as soon as it is turned on (booting). The term “firmware” means that software is stored in hardware on a permanent basis.

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ROM lookup tables – storage of trigonometric functions and code conversion tables, which do not change. e.g. instead of performing a calculation each time a function such as sine, cosine, etc. is needed, the microprocessor simply looks up the value associated with the function in a ROM table.

2. RAM MemoryThe computer uses the RAM portion of primary memory to hold programs and data currently being executed by the microprocessor. Note that:

Random Access means that any address location in the memory can be accessed as quickly as another location.

RAM is fast enough to work directly with the microprocessor without slowing it down too significantly.

During the execution of a program, RAM address locations store the intermediate or final results of processing.

All RAM has the disadvantage of being volatile. This means that any data stored in RAM is lost if power to the computer is disrupted for any reason.

2.4.3. Secondary Storage Media and Devices

Slower, less expensive forms of memory, called Secondary storage are used for long-term storage of programs and data, or to hold masses of programs and data too large to be held in the Primary memory. The main emphasis for Secondary storage devices is the capability to store large amounts of data on a permanent, or semi-permanent basis, as cheaply as possible. The materials (tape, disk, paper, cards, etc) used to store information in secondary storage devices are collectively called Media.

Secondary storage is to be too slow to be used directly with the computer’s microprocessor. The secondary memory unit holds the information and transfers it in batches to the computer’s faster internal memory when requested. A buffer may be used in these situations to compensate for varying speeds.

For our purposes, when we describe the characteristics of a storage medium the following areas should be considered:

1. Physical description of the medium.2. How is data stored on the medium?3. Which device writes to/reads from the medium?4. Storage capacity (in bytes) of the medium.5. Type of access method - Serial or random access? 6. Advantages/disadvantages associated with the use of the medium.7. How does it compare with other media?

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Common storage Media:The following is a list of some of the popular storage media:

Magnetic Media:Magnetic tape A storage medium consisting of a flexible plastic strip covered with

magnetic material on one side, used to store data. Sequential access.

capable of storing large amounts of data and information at a low cost;

A tape drive reads from and writes data and information on a tape;

A tape cartridge is a small, rectangular, plastic housing for tape used in today’s tape drives;

Used by business and home users to backup personal computer hard disks;

Both external and internal tape units for personal computers. Larger computers use tape cartridges mounted in a separate cabinet called a tape library

Magnetic Disks:

1. Floppy disk A flexible magnetic coated disk, commonly used with microcomputers, on which data can be stored magnetically. Random access method used to access data. Storage capacity - 760MB or 1.2MB

Device: uses a Floppy Disks Drive (FDD)

A device that can read from and write on a floppy disk Contains a read/write head, which is able to access (read) data

from and place (write) data on a magnetic disk any number of times.

2. Micro-floppy disk

Refers to 3.5" floppy disks. A storage medium, which consists of a thin, circular, flexible plastic material with a magnetic coating and enclosed in a square-shaped plastic shell.Characteristics: A portable, inexpensive storage medium; Classified as magnetic media; standard disk size is 3.5” in

diameter. They are housed in rigid plastic casting having a sliding shutter

covering an opening to the recording surface; This automatically closes when the disk is removed from the disk drive.

Has a small opening (called a write protect notch) with a cover that you slide up or down protects floppy disks from accidentally being erased.

A typical floppy disk stores data on both sides of the disk Random access medium. Most floppy disks today are high density (HD) with a capacity

of 1.44 MB

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That is # of bytes on a disk = 80 tracks per side x 18 sectors per track x 2 sides per disk

x 512 bytes per sector = 1,474,560 bytes = 1.47 GB

4. ZIP disk, Jaz disk, SparQ disk

Disks that can store 100MB, 1GB and 1GB respectively. Random access media.

5. Hard disk A rigid metallic disk used for storing data magnetically.Charateristics: Its rigid construction allows for higher storage densities. Access times for a hard disk are much faster than for floppy

disks. A hard disk spins constantly, while a floppy disk starts spinning only when it receives a read or write command.

Random access medium. Typically stores 1 to 40 GB. Contains more than one platter. Tracks are arranged in

cylinders.Hard disks maybe:

Optical disk is a storage medium in which laser technology is used to etch the surface of the disk, forming minute patterns which represent data.e.g. (CD-ROM, compact disk, (650 MB) and DVD-ROM, digital video disk, (5 GB)Random access.Characteristics: A flat, round, portable, metal storage medium that usually is

4.75 inches in diameter and less than one-twentieth of an inch thick.

A compact disc typically stores items in a single track; It spirals from the center of the disc to the edge of the disc; The track is divided into evenly sized sectors in which items are stored

Massive storage capacity High quality sound and pictures possible Reliable - little deterioration of quality of data even after

continuous use entirely unaffected by magnetic fields

a. CD-ROMs A silver-colored compact disc that uses the same laser technology as audio CDs for recording music; Can contain text, graphics, audio, and video.Characteristics: The manufacturer writes, or records, the contents of standard

CD-ROMs A CD-ROM drive or CD-ROM player is used to read items on a

CD-ROM A typical CD-ROM holds about 650 MB of data, instructions,

and information Manufactures use CD-ROMs to store and distribute today’s

multimedia software and other complex softwareTypes available:CD-R (compact disc-recordable)

A multi-session compact disc onto which you can record your own items such as text, graphics, and audio.

You write on the CD-R using a CD recorder or a CD-R

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drive and special software.CD-RW - (compact disc-rewritable)

An erasable disc you can write on multiple times; You must have CD-RW software and a CD-RW drive.

b. DVD-ROM (digital video disc-ROM)

An extremely high capacity compact disc capable of storing from 4.7 GB to 17 GB.

You must have a DVD-ROM drive or DVD player to read a DVD-ROM

Looks just like a CD-ROM but data, instructions, and information is stored in a slightly different manner to achieve a higher storage capacity.

c. Magneto Optical Disk

A hybrid between magnetic disks and optical disks.  i.e. A type of disk drive that combines magnetic disk technologies with CD-ROM technologies. Data are written to a disk using a laser beam and a magnetic read\write-head

A portable high storage capacity - more than 200 megabytes that can be read from and written to.

considerably more expensive than CD-ROMs to implement

3. Microfilm and Microfiche

Store microscopic images of documents on roll or sheet film Images recorded onto film using a computer output microfilm

(COM) recorder Images can only be read with a microfilm or microfiche reader Microfilm and microfiche are inexpensive and have the longest

life of any storage medium

Comparison between Primary and Secondary Storage

Secondary Storage (also called auxiliary storage, permanent storage, or mass storage)

the media on which data, instructions, and information are kept, as well as the devices that record and retrieve these items.

Function:o Nonvolatile Storage - Permanent storage of data, programs, instructions, and

information for future use;o Back-up - can be used to backing-up data;

Primary Storage:

A temporary holding place for data and instructions; Consists of one or more chips on the motherboard; Made up of RAM, ROM;

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