A Computer is an electronic data processing machine that accepts data, processes them and gives the result/output (i.e. the meaningful information). Basically, a Computer is a machine that can store instructions and execute them. A computer is a machine, so it cannot work itself. A computer performs according to the instructions given by the user. It can perform calculations, draw pictures, read and write data, and do many other works.

          The computer can be classified on the following four basis:

1. On the basis of Performance/Work
2. On the basis of Size
3. On the basis of Brand
4. On the basis of Technology/Model

          On the basis of Performance, the computer can be classified in the following three types:

1. Analog Computer
2. Digital Computer
3. Hybrid Computer

a. Analog Computer

          The computer that measures physical values (such as temperature, pressure, current, etc.) is known as Analog Computer. This computer represents values as a continuously varying voltage/value. For example, a Speedometer shows changes in speed using a needle indicator that can move over an infinite range of speeds up to the maximum limit of the vehicle.

b. Digital Computer

          The computer that performs using/counting the digits 0 and 1 is known as Digital Compute. This computer represents information in discrete form. It is used to perform calculations, draw pictures, etc. The computer you use is Digital Computer.

c. Hybrid Computer

          The computer made by using the combination of both analog and digital computers is known as Hybrid Computer. This computer can do the tasks of digital as well as analog computers. The hybrid computers attached to the jet planes help the pilots to fly days and nights without any trouble. During the flight, the hybrid computer determines the altitude, air pressure, humidity, distant mountain, landing zone, length of runway, etc.

          On the basis of Size, the computer can be classified in the following four types:

1. Mainframe Computer
2. Mini Computer
3. Micro Computer
4. Super Computer

a. Mainframe Computer

          A large and multiuser computer that is designed to meet the computing needs of a large organization is known as Mainframe Computer. The mainframe computer can be used by 100 to 500 users at one time.

b. Mini Computer

          A medium-sized and multiuser computer that is designed to meet the computing needs of a small organization, or a department is known as Mini Computer. The mini computer can be used by 50 to 100 users at one time.

c. Micro Computer

          A computer that is made by using the microprocessor is known as Micro Computer. Micro Computer can be used by one person at a time.

d. Super Computer

          A computer that is designed to run faster than ordinary Mainframe computer is known as Super Computer. The example of Super Computer is Robert.

          On the basis of Brand, the computer can be classified in the following three types:

1. IBM Computer
2. IBM Compatible Computer
3. Apple/Macintosh Computer

a. IBM Computer

          IBM stands for International Business Machine. A computer that is manufactured by IBM Corporation is known as IBM Computer. This computer is of the original brand. It is expensive compared to IBM Compatible Computer.

b. IBM Compatible Computer

          A computer that is manufactured on the principle of IBM Computer is known as IBM Compatible Computer. It is less expensive than IBM Computer.

c. Apple/Macintosh Computer

          A computer that is manufactured by Apple/Macintosh Corporation is known as Apple/Macintosh Computer. In Apple/Macintosh Computer, the CPU and Monitor are fixed while they are separate in IBM and IBM Compatible Computers. The Mouse is compulsory in this computer.

          On the basis of Technology, the computer can be classified in the following three types:

1. XT (Extended Technology) Computer
2. AT (Advanced Technology) Computer
3. PS/2 (Personal System/2) Computer

a. XT Computer

          A computer that is made by using the 8080, 8086, or 8088 microprocessor is known as XT Computer.

b. AT Computer

          A computer that is made by using the 80286, 80386, 80486, or Pentium microprocessor is known as AT Computer.

c. PS/2 Computer

          In 1990, IBM Corporation developed a computer as the new brand, which is known as PS/2 Computer. All the laptop computers made after 1990 come under PS/2 Computer.

Block Diagram of Computer

      View Image

          All the components of a computer that we can see and feel are known as Hardware. For example, Keyboard, Mouse, CPU, Monitor, Printer, etc.

          A program that makes a computer perform is known as Software. In other words, software is a set of instructions that tells a computer what to do. Without software, a computer is useless.

          On the basis of performance, there are three types of software:

1. Application Software:
1. Standard Application Software
2. Tailored Application Software


2. System Software
3. Utility Software

          The software that is common for all users is known as Standard Application Software. This software does actual work for the user. This types of software are ready-made and are available in the market. The examples of Standard Application software are MS Word, MS Excel, Adobe Pagemaker, etc.

          The software that is developed for a specific client/firm for the purpose of a specific task is known as Tailored Application Software. This software is developed as per the requirements of the clients/firms. The examples of Tailored Application software are FACT Accounting, Tally, Producing bills in Department Store, etc.

          The software that is needed to operate a computer is known as System Software. This software creates an environment for the user to run other software programs and do different works. System Software is also called Operating System.

          The software that maintains a computer is known as Utility Software. The examples of Utility software are Scan Disk, Data Compression, NDD, Norton Anti-virus, etc.

          An Operating system is a master program of the computer that controls the computer's basic functions. The operating system manages hardware and software resources of the computer. It works (serves) as the interface between the user and the computer, and between the computer hardware and other software programs. The examples of Operating System are MS-DOS, Windows 98/2000, Windows NT, etc. There are two types of operating system:

1. Single User Operating System
2. Multi-user Operating System

          The operating system that allows only one person to access programs and data/information at the same time is known as Single User Operating System. MS-DOS, Windows 98, Windows 2000, etc. are the examples of Single User Operating System.

          The operating system that allows more than one person to access programs and data/information at the same time is known as Multi-user Operating System. In Multi-user System, each user is equipped with a terminal. Windows NT, Windows 2000 Server, etc. are the examples of Multi-user Operating System.

          Booting means starting up a computer. The process of loading (transferring) the system files (i.e. IO.SYS, MSDOS.SYS, and COMMAND.COM.) into the memory of the computer from a disk is known as Booting (or Boot). There are two types of booting/boot:

1. Cold Boot
2. Warm Boot (Hot Boot)

          The process of starting up a computer that has been completely shut down is known as Cold Boot.

          The process of restarting a computer that has been already running is known as Warm Boot. Sometimes the computer is in "Hang" position, at that time you have to do Warm boot. Warm Boot is done by either pressing the RESET button or pressing the CTRL+ALT+DELETE keys at the same time.

          Any component or part of a computer connected to it is known as Device. A Device is also called a Peripheral. Printer, Mouse, Keyboard, etc. are the examples of a device.

          A Device Driver is a program that makes a device work. In other words, a Device Driver is a file that provides the operating system with information needed for operating a device.

          In a computer, there are four methods of counting, which are as follows, including the symbols and base:

SN	Method	Symbol	Base
1	Decimal (Number) System	0-9	10
2	Binary (Number) System	0,1	2
3	Octal (Number) System	0-7	8
4	Hexa-decimal (Number) System	0-9,A-F	16

EDP (Electronic Data Processing)
ASCII (American Standard Code for Information Interchange)

A-----> 65 -----> 1000001

Conversion from Binary to Decimal

1	0	0	0	0	0	1
6	5	4	3	2	1	0
= 26×1 + 25×0 + 24×0 + 23×0 + 22×0 + 21×0 + 20×1 = 65

          In a computer, the measuring units are used to measure the storage (memory) capacity and the size/length of a program/file, etc. For example, Bits, Nibble, Byte, Word, etc.

          Bits (i.e. Binary Digits) are the smallest unit of information. A Nibble is a group of 4 bits. A Byte is a group of 8 bits . A Word is a group of 2 or more bytes (16 bits = 2 bytes).

		Bit       = 1 or 0
		4 bits    = 1 Nibble
		8 bits    = 1 Byte (or character)
		2 bytes   = 1 Word

		1024 bytes     = 1 Kilobytes (K)
		1024 Kilobytes = 1 Megabytes (MB)
		1024 Megabytes = 1 Gigabytes (GB)
		1024 Gigabytes = 1 Terabytes