Introduction of Computer

Introduction

What is a Computer?

Definition:

A computer is an electronic machine that

1) Takes in data and instructions (input)

2) Works with the data (processing)

3) Puts out information (output)

A general-purpose machine that processes data according to a set of instructions

that are stored internally either temporarily or permanently.

A simple computer may look like this:

Memory (RAM) -- used to store values during execution of a program,

CPU (Central Processor Unit) -- does the `work',

Disc drive -- `permanently' stores files,

Keyboard -- allows user to input information,

VDU -- visually outputs data,

What is Computer Science?

Computer Science is the systematic study of algorithmic processes that describe

and transform information: their theory, analysis, design, efficiency, implementation, and

application.

Algorithm - A finite sequence of steps that solves a problem.

input -->pro c --> output

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Computer Generations

First-generation computers, starting with the UNIVAC I in 1951, used vacuum

tubes, and their memories were made of thin tubes of liquid mercury and magnetic

drums.

Second-generation systems in the late 1950s replaced tubes with transistors and

used magnetic cores for memories (IBM 1401, Honeywell 800). Size was reduced and

reliability was significantly improved.

Third-generation computers, beginning in the mid-1960s, used the first integrated

circuits (IBM 360, CDC 6400) and the first operating systems and DBMSs.

Starting in the mid-1970s, the fourth generation brought us computers made

entirely of chips. It spawned the microprocessor and personal computer. It introduced

distributed processing and office automation.

The fifth generation implies faster hardware and more sophisticated software that

uses artificial intelligence (AI) routinely. Natural language recognition is a major

component of the fifth generation.

What is Hardware and Software?

The computer and all equipment attached to it are called hardware. The

instructions that tell it what to do are called "software." A set of instructions that perform

a particular task is called a "program" or "software program."

Hardware is the physical medium, for example:

Circuit boards

Processors

Keyboard

Software is computer programs, for example:

Operating system

Editor

Compilers

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A Fortran 90 program

Hardware Components

Input Devices -- "How to tell it what to do"

A keyboard and mouse are the standard way to interact with the computer. Other

devices include joysticks and game pads used primarly for games.

Output Devices -- "How it shows you what it is doing"

The monitor (the screen) is how the computer sends information back to you,

whether it be surfing the web or writing a memo. A printer is also an output device.

Storage Devices -- "How it saves data and programs"

Hard disk drives are an internal, higher capacity drive which you also stores the

operating system which runs when you power on the computer.

"Floppy" disk drives allow you to save work on small disks and take the data with you

Memory -- "How the processor stores and uses immediate data"

When you use a program, the computer loads a portion of the program from the

hard drive to the much faster memory (RAM). When you "save" your work or quit the

program, the data gets written back to the hard drive.

Microprocessors -- "The brain of the computer"

PCs primarily use microprocessors (sometimes called the chip) manufactured byIntel. The older Intel versions include the 386, 486 and now the Pentium line.

- Macintoshes use PowerPC processors by Motorola.

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Megahertz (MHz) is the internal processor speed in which computer instructions

are performed. The MHz speed does not always indicate the power of the

microprocessor. Newer processors can execute more instructions at the same or slower

MHz. For example, an Intel 486 @100MHz is less powerful than a Pentium @75 MHz

(but the MHz is "faster").

Hardware Accessories

Modems

Modems allow you to communicate with other computers using a phone line.

Modem speeds are in bits per second (14.4, 28.8 and 56 thousand bits per second are

standard).

CD-ROM Drives

A CD-ROM drive is a high capacity storage device which lets you read data from

the disk, but not writes data back. The speed of the drive (how fast the CD platter spins)

is measured in multiples from the first generation drives. New drives are up to 24X (or 24

times the first drives), but while the CD spins faster, it is not really 24 times faster in

actual output.

Printers

There are different types of printers (laser, ink jet, dot matrix) with differing

quality of output. They are measured in dpi (dots per inch) and ppm (pages per minute),

the higher the better.

Scanners

Scanners "digitize" printed material (like photos and graphics) and save it to a

graphic file format (like .GIF or .JPG) for display on the computer.

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Operating System Software

Operating system software provides a "user interface" for users to manage files,

start programs, customize computer settings, and other tasks. The operating system also

provides the fundamental core computer functionality for programmers.

Intel based PCs use Microsoft Windows version 3.1 (older) or Windows 95 as the

operating system. Macintoshes use the Macintosh operating system.

Software Applications

Application software uses the operating system software and provides the real

functionality of a computer. Applications include:

Word Processing (MS Word, WordPerfect, Ami...)

Spreadsheets (Lotus 123, MS Excel...)

Database (DBase, Fox Pro, Oracle...)

Presentation (MS PowerPoint, Persuasion...)

Internet Browsers (Netscape Navigator, MS Internet Explorer)

Games

Windows Versions

Windows Vista- for home and business desktops and portable computers

Windows Server 2003 for servers

Small Business Server for first server installations (up to 2 processors)

Web Edition for basic Web serving (up to 2 processors)

Standard Edition for smaller server applications that don't require clustering (up to 4 processors)

Enterprise Edition for larger server applications, and clustering (up to 8 processors)

Datacenter Edition for mainframe like servers (up to 128 processors)

Storage Server for Network Attached Storage Devices

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Windows XP Embedded, for embedded systems requiring parts of the Windows XP infrastructure

Windows Fundamentals for Legacy PCs, a low-end version of Windows XP that is intended to be a thin-client that works with older hardware.

Windows Embedded CE 6.0, for embedded systems (not based on the Windows NT kernel)

Windows XP for desktops and laptops (notebooks)

Windows XP Starter Edition, for new computer users in developing countries

Windows XP Home Edition, for home desktops and laptops

Windows XP Professional Edition, for business and power users

Windows XP Media Center Edition for desktops and notebooks with an emphasis on audio and video.

Windows 2000, Windows Me, Windows 98, Windows NT 4.0 - the last version which

ran on RISC architectures like PowerPC, Windows 95, Windows NT 3.5,Windows

3.2,Windows NT 3.1,Windows 3.1,Windows 3.0, Windows 2.0, Windows 1.0.

Operating System

Introduction

Operating system is the most important program that runs on a computer.

Every general-purpose computer must have an operating system to run other

programs.

Operating systems perform basic tasks, such as recognizing input from the

keyboard, sending output to the display screen, keeping track of files and

directories on the disk, and controlling peripheral devices such as disk drives and

printers.

The operating system is also responsible for security, ensuring that unauthorized

users do not access the system.

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Operating systems can be classified as follows:

Multi-User: Allows two or more users to run programs at the same time. Some

operating systems permit hundreds or even thousands of concurrent users.

Multiprocessing: Supports running a program on more than one CPU.

Multitasking: Allows more than one program to run concurrently.

Multithreading: Allows different parts of a single program to run concurrently.

UNIX Introduction

What is UNIX?

UNIX is an operating system which was first developed in the 1960s, and

has been under constant development ever since.

It is a stable, multi-user, multi-tasking system for servers, desktops and

laptops.

UNIX systems also have a graphical user interface (GUI) similar to Microsoft

Windows which provides an easy to use environment.

Types of UNIX

There are many different versions of UNIX, although they share common similarities.

The most popular varieties of UNIX are Sun Solaris, GNU/Linux, and Macos X.

The UNIX operating system

The UNIX operating system is made up of three parts; the kernel, the shell and

the programs.

The kernel

The kernel of UNIX is the hub of the operating system: it allocates time and

memory to programs and handles the filestore and communications in response to

system calls.

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As an illustration of the way that the shell and the kernel work together, suppose

a user types rm myfile (which has the effect of removing the file myfile). The shell

searches the file store for the file containing the program rm, and then requests the

kernel, through system calls, to execute the program rm on myfile. When the process rm

myfile has finished running, the shell then returns the UNIX prompt % to the user,

indicating that it is waiting for further commands.

The ShellThe shell acts as an interface between the user and the kernel. When a user logs

in, the login program checks the username and password, and then starts another program

called the shell. The shell is a command line interpreter (CLI). It interprets the commands

the user types in and arranges for them to be carried out. Filename Completion - By

typing part of the name of a command, filename or directory and pressing the [Tab] key,

the shell will complete the rest of the name automatically. If the shell finds more than one

name beginning with those letters you have typed, it will beep, prompting you to type a

few more letters before pressing the tab key again. History - The shell keeps a list of the

commands you have typed in. If you need to repeat a command, use the cursor keys to

scroll up and down the list or type history for a list of previous commands.

Files and processes

Everything in UNIX is either a file or a process.

A process is an executing program identified by a unique PID (process identifier).

A file is a collection of data. They are created by users

Widely used Unix commands include:

Directory and file creation and navigation: ls cd pwd mkdir rm rmdir cp find

touch

File viewing and editing: more less ed vi emacs head tail

Text processing: echo cat grep sort uniq sed awk cut tr split printf

File comparison: comm cmp diff patch

Miscellaneous shell tools: yes test xargs

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System administration: chmod chown ps su w who

Communication: mail telnet ftp finger ssh

Authentication: su login passwd

LINUX

IntroductionLinux is a Unix-like computer operating system. Linux is one of the most

prominent examples of free software and open source development; its underlying source

code can be freely modified, used, and redistributed by anyone.[1]

The Linux kernel was first released to the public on 17 September 1991, for the

Intel x86 PC architecture.

The kernel was augmented with system utilities and libraries from the GNU

project to create a usable operating system, which later led to the alternate term

GNU/Linux.[2].

Properties of Linux

Linux is free:

If you want to spend absolutely nothing, you don't even have to pay the price of a

CD. Linux can be downloaded in its entirety from the Internet completely for free.

No registration fees, no costs per user, free updates, and freely available source

code in case you want to change the behavior of your system.

Linux is portable to any hardware platform:

A vendor who wants to sell a new type of computer and who doesn't know what

kind of OS his new machine will run (say the CPU in your car or washing

machine), can take a Linux kernel and make it work on his hardware, because

documentation related to this activity is freely available.

Linux was made to keep on running:

As with UNIX, a Linux system expects to run without rebooting all the time.

Linux is secure and versatile:

Linux is scalable:

From a Palmtop with 2 MB of memory to a petabyte storage cluster with

hundreds of nodes: add or remove the appropriate packages and Linux fits all.

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Mac OSXIntroduction

Mac OS X Apple's Upcoming Mac OS X v10.5 ("Leopard")

Mac OS X is a line of proprietary, graphical operating systems developed,

marketed, and sold by Apple Inc., Mac OS X is the successor to the original Mac

OS, which had been Apple's primary operating system since 1984.

The operating system was first released in 1999 as Mac OS X Server 1.0, with a

desktop-oriented version (Mac OS X v10.0) following in March 2001. Since then,

four more distinct "end-user" and "server" editions of Mac OS X have been

released, the most recent being Mac OS X v10.4, which was first made available

in April 2005. Releases of Mac OS X are named after big cats; Mac OS X v10.4

is usually referred to by Apple and users as "Tiger". In October 2007, Apple will

release Mac OS X 10.5, nicknamed "Leopard".

Internet and NetworkIntroduction

What is an internet?

The Internet is a computer network made up of thousands of networks worldwide.

No one knows exactly how many computers are connected to the Internet.

All computers on the Internet communicate with one another using the

Transmission Control Protocol/Internet Protocol suite, abbreviated to TCP/IP.

Computers on the Internet use a client /server architecture.

How Does the Internet Work?

The Internet is a worldwide collection of computer networks, cooperating with

each other to exchange data using a common software standard. Through telephone

wires and satellite links, Internet users can share information in a variety of forms.

The size, scope and design of the Internet allows users to:

Connect easily through ordinary personal computers and local phone

numbers.

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Exchange electronic mail (E-mail) with friends and colleagues with

accounts on the Internet.

Post information for others to access, and update it frequently.

Access multimedia information that includes sound, photographic images

and even video and

Access diverse perspectives from around the world.

The History of the Internet

The Internet began as ARPAnet, a U.S. Department of Defense project.

During the next two decades, the network that evolved was used primarily by

academic institutions, scientists and the government for research and

communications.

The nature of the Internet changed abruptly in 1992, when the U.S. government

began pulling out of network management, and commercial entities offered

Internet access to the general public for the first time.

What Kinds of Information are Available?

In addition to text documents, the Internet makes available graphics files

(digitized photographs and artwork), and even files that contain digitized sound

and video.

Through the Internet, you can download software, participate in interactive

forums where users post and respond to public messages, and even join "chats," in

which you and other users type (and, in some cases, speak) messages that are

received by the chat participants instantly.

Components of the Internet

The most popular and important systems are:

E-mail, for exchange of electronic mail messages.

USENET newsgroups, for posting and responding to public "bulletin board"

messages.

File Transfer Protocol (FTP), a system for storing and retrieving data files on

large computer systems.

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Gopher, a method of searching for various text-based Internet resources (largely

obsolete).

TELNET, a way of connecting directly to computer systems on the Internet.

Internet Relay Chat (IRC), a system for sending public and private messages to

other users in "real time"—that is, your message appears on the recipient's screen

as soon as you type it.

CU-SeeMe, a videoconferencing system that allows users to send and receive

sound and pictures simultaneously over the Internet.

The World Wide Web, The World Wide Web provides a single interface for

accessing all these protocols.

World Wide Web

The official definition of the WWW is "wide-area hypermedia information

retrieval initiative aiming to give universal access to a large universe of

documents."

Wide-area: The World Wide Web spans the whole globe.

Hypermedia: It contains various types of media (text, pictures, sound, movies ...) and

hyperlinks that connect pages to one another.

Information retrieval: Viewing a WWW document (commonly called a Web page) is

very easy thanks to the help of Web browsers. They allow you to retrieve pages just by

clicking links, or entering addresses.

Universal access: It doesn't matter what type of computer you have, or what type of

computer the page you want is stored on - your Web browser allows you to connect

seamlessly to many different systems.

Large universe of documents: Anyone can publish a Web page - and nearly

anyone has! No matter what obscure information you want to find, there is bound

to be someone out there who has written a Web page about it.

Application of internet

1. Electronic mail

2. File transfer

3. Interactive collaboration

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4. Real-time broadcasting

5. Breaking news

6. Shopping opportunities

7. Multimedia displays

Network

A network is a number of computers connected together to share information and hardware.

LAN, WAN and Other Area Networks

One way to categorize the different types of computer network designs is by their

scope or scale. For historical reasons, the networking industry refers to nearly every type

of design as some kind of area network. Common examples of area network types are:

LAN - Local Area Network, WLAN - Wireless Local Area Network,

WAN - Wide Area Network, MAN - Metropolitan Area Network,

SAN - Storage Area Network, CAN - Campus Area Network, PAN - Personal Area

Network, DAN - Desk Area Network.

A LAN (local area network) is a group of computers and network device

connected together, usually within the same building. By definition, the connections must

be high speed and relatively inexpensive (e.g., token ring or Ethernet). A WAN (wide

area network), in comparison to a MAN, is not restriced to a geographical location,

although it might be confined within the bounds of a state or country. A WAN connects

several LANs, and may be limited to build an enterprise (a corporation or an

organization) or accessible to the public. The technology is high speed and relatively

expensive. The Internet is an example of a worldwide public WAN.

Scanners

Scanners are peripheral devices used to digitize (convert to electronic format)

artwork, photographs, text, or other items from hard copy. In a sense, a scanner works as

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a pair of eyes for your PC. Your eyes see an image and translate the image into electrical

impulses that travel to and are interpreted by your brain. Similarly, a scanner captures

images and converts them to digital data that travel to and are interpreted by the

computer.

A scanner works by dividing an image into microscopic rows and columns and

measuring, like the film in a camera, how much light (or lack thereof) reflects from each

individual intersection of the rows and columns. Each reflection is recorded as a dot, or

picture element (pixel). After the scanner collects information from each dot, it compiles

the result into a digital file on the computer.

There are a wide variety of scanners that work in a number of different ways, but

the technology behind them is essentially the same.

More popular types of scanners

Flatbed Scanners

Flatbed scanners look and behave a lot like a photocopier. You lay the item to be

scanned on a glass plate and the scanning head passes below the glass.

Flatbed scanners are very versatile: you can scan objects in a variety of sizes and

shapes, including pages from a book, without damaging the original. While flatbed

scanners are the best choice for a wide variety of uses, if you plan to do a lot of text

scanning (called OCR for Optical Character Recognition) work, keep in mind that

flatbeds only accommodate one page at a time. Scanning multi-page documents can be a

slow, tedious process, because you have to manually remove one page and insert the

next.

Sheetfed Scanners

Sheetfed scanners look and act more like fax machines. The page or item is fed

into the machine, scanned, then spit out on the other end . A sheetfed scanner is a good

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choice for large volumes of text, but not for handling delicate original photographs.

Scanning directly from a book or other three-dimensional object is impossible.

Hand Scanners

Hand scanners are a low-cost alternative to their larger, more sophisticated

cousins. As their name implies, hand scanners are manual devices you move over a flat

surface, just as you do your PC's mouse

The hand scanner's advantages are many, but so are its disadvantages. Generally,

hand scanners work best for small, uncomplicated images such as company logos or

small black-and-white photographs. You might want a hand scanner if you don't plan to

use it on a regular basis, because it usually doesn't require adding internal cards to your

CPU, and it's easily disconnected and stored away. Most hand scanners can only scan a

four-inch wide image at one time and require a steady hand. You're usually provided with

software that helps you "sew up" a series of these 4-inch, side-by-side scans into one

image, but this is obviously not as convenient as getting the full image at once.

NOTE: Other types of scanners also exist, such as barcode readers (like the ones at the

grocery checkout) and slide scanners; however, because these are specialty items

primarily used for commercial purposes, they are not covered here.

Color versus Grayscale Scanners

Scanners that can scan images in full color have become much more popular as

their prices have dropped. Just a few years ago, color scanners cost several thousands of

dollars, but can now be bought for a few hundred, depending on resolution and type.

Even so, grayscale (meaning shades of black and white only, no color) scanners

are still available and are significantly cheaper. In many cases, they are perfectly

adequate for the average user. Unless you have a color printer, or use your scanner to

create artwork that will only be viewed on-screen (such as for a Web page), there's no

point in having a color scanner. Consider this carefully before buying; however, what you

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think you'll never do now could change as you grow more experienced and interested in

computer technology.

VIRUS

A program or piece of code that is loaded onto your computer without your

knowledge and runs against your wishes.

Viruses can also replicate themselves. All computer viruses are manmade.

A simple virus that can make a copy of itself over and over again is relatively

easy to produce.

Even such a simple virus is dangerous because it will quickly use all available

memory and bring the system to a halt.

An even more dangerous type of virus is one capable of transmitting itself across

networks and bypassing security systems.

A worm is similar to a virus by its design, and is considered to be a sub-class of a

virus. Worms spread from computer to computer, but unlike a virus, it has the capability

to travel without any help from a person.

A Trojan Horse is full of as much trickery as the mythological Trojan Horse it

was named after. The Trojan Horse, at first glance will appear to be useful software but

will actually do damage once installed or run on your computer.

Computer Maintenance

The role of software development

Because software is often designed with security features to prevent unauthorized

use of system resources, many viruses must exploit software bugs in a system or

application to spread. Software development strategies that produce large numbers of

bugs will generally also produce potential exploits.

Anti-virus software and other preventive countermeasures

There are two common methods that an anti-virus software application uses to

detect viruses. The first, and by far the most common method of virus detection is using a

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list of virus signature definitions. The disadvantage of this detection method is that users

are only protected from viruses that pre-date their last virus definition update. The second

method is to use a heuristic algorithm to find viruses based on common behaviors. This

method has the ability to detect viruses that anti-virus security firms’ have yet to create a

signature for.

Many users install anti-virus software that can detect and eliminate known viruses

after the computer downloads or runs the executable. They work by examining the

content heuristics of the computer's memory (its RAM, and boot sectors) and the files

stored on fixed or removable drives (hard drives, floppy drives), and comparing those

files against a database of known virus "signatures". Some anti-virus programs are able to

scan opened files in addition to sent and received emails 'on the fly' in a similar manner.

This practice is known as "on-access scanning."

Anti-virus software does not change the underlying capability of host software to

transmit viruses. Users must update their software regularly to patch security holes. Anti-

virus software also needs to be regularly updated in order to gain knowledge about the

latest threats.

Preventive Methods

One may also prevent the damage done by viruses by making regular backups of

data (and the Operating Systems) on different media, that are either kept unconnected to

the system (most of the time), read-only or not accessible for other reasons, such as using

different file systems.

Recovery methods

Once a computer has been compromised by a virus, it is usually unsafe to continue

using the same computer without completely reinstalling the operating system. However,

there are a number of recovery options that exist after a computer has a virus. These

actions depend on severity of the type of virus.

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Virus removal

One possibility on Windows XP is a tool known as System Restore, which

restores the registry and critical system files to a previous checkpoint. Often a virus will

cause a system to hang, and a subsequent hard reboot will render a system restore point

from the same day corrupt. Restore points from previous days should work provided the

virus is not designed to corrupt the restore files. Some viruses, however, disable system

restore and other important tools such as Task Manager and Command Prompt. Examples

of viruses that do this would be CiaDoor.

Operating system reinstallation

As a last ditch effort, if a virus is on your system and anti-viral software can't

clean it, then reinstalling the operating system may be required. To do this properly, the

hard drive is completely erased (partition deleted and formatted) and the operating system

is installed from media known not to be infected. Important files should first be backed

up, if possible, and separately scanned for infection before erasing the original hard drive

and reinstalling the operating system.

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