Computer, Parts of a Computer, Some Important Definitions and Short Notes

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“The word Computer is derived from compute which means to calculate. In simple and technical term it is an automatic electronic calculating machine that processes or manipulates a given data according to a program or set of instructions and gives a desired output.”

Parts of a Computer

The computer is composed of two parts:

1) Hardware

2) Software


All physical components of computer, which can be touched, measured, have weight and occupy space, are collectively called computer hardware viz;

  • Keyboard

  • Mouse

  • Joy stick

  • Scanners

  • Monitor

  • Printer

  • Central Processing unit etc.


  • Software can be defined as a set of instructions or codes written in a defined manner. In other words software’s are prewritten programs, which control the operations of computer.

  • OR All programs and data stored on floppy disk, Hard disk, CD-ROM are collectively called softwares. Examples are;

    • DOS

    • Window

    • UNIX

    • XENIX

    • Linus

    • Java

    • MS Office

Devices or Components of a Computer

The computer is a combination of many parts, each of which performs specific task independently. The major devices of a computer are as under.

  • Input Devices The input devices are those devices which send data or information to the Central Processing Unit. The main input devices are:

    • Keyboard: It is used to enter text. It contains alphabetic, numeric and other keys for entering data.

    • Mouse: It is a pointing device. It controls the pointer on the screen.

    • Microphone: It is used to enter voice into the computer.

    • Scanner: It reads printed text and graphics and then translates the result into digital form.

    • Digital Camera: It is used to take photos.

    • PC Camera: It is used to create movie and to take photos on the computer.

  • Out Put Devices: A hardware component used to display information to the user output device.

    • Monitor: It is used to display text, graphics and video output.

    • Printer: It is used to display printed output on paper.

    • Speaker: It is used to hear sound to hear sound music and voice outputs.

  • Storage Device: The hardware components used to store data, instructions and information permanently are called storage devices. For example floppy disk drive, zip drive, hard disk drive, CD-ROM drives etc.

  • Communication Devices: It is used to communicate and exchange data, instructions and information with other computers. For example Modem.


  • ALU (ARTHMETIC AND LOGICAL UNIT) ALU is a part of CPU. Actual execution of instructions takes place in this part. All arithmetic and logical operations are performed in ALU. It consists of two units:

    • Arithmetic Unit It performs basic arithmetic functions such as addition, subtraction, division.

    • Logical Unit It performs logical operations like comparing two data items to find which data item is greater than, equal to, or less than the other.

    • CONTROL UNIT It acts like a supervisor of the computer. It does not execute program instruction by itself. It controls and coordinates all activities of computer system.

    • Memory Unit (MU) it is responsible for storage of data and information. The memory unit consists of two types of memory which are RAM and ROM.

Some Important Definitions and Short Notes


RAM stands for random access memory. It is that part of CPU where temporary information is stored.


  • A group of 8 bits is called a byte.

  • Icons: Pictorial objects on the desktop or screen are called Icons.


It is an input device, normally called a ―Pointing device‖. This device is used for pointing anything on monitor through a blinking cursor.


  • A set of instructions or codes written in a defined manner or prewritten programs which control the operations of computer.

Control Unit

A unit of CPU which is responsible for all automatic operations carried out by the digital computers is called CU. The CU directs and coordinates all activities of a computer.


LAN stands for local area network. It is privately owned communication network that serves users within a confirmed geographical area. The range is usually within a mile-perhaps one office, one building or a group of buildings.


It stands for wide area network. It is a communication network that covers a wide geographical area. The range is usually a state or a country. Examples are Telenet, Uninet etc.


  • Modem is abbreviation of Modulate-de-Modulate. Modulation is a process that converts digital signals into Analog form and Demodulation is a process that converts Analog signals into digital form.

  • The device which performs modulation and demodulation is called a MODEM. In simple words it is a device that converts the digital signals into Analog and then back from Analog to digital form.


A unit of CPU that performs arithmetic and logical operations is called ALU.


  • Registers are high-speed staging areas that temporarily store data during processing and provide working areas for computation. Registers are contained in control unit and arithmetic Logic Unit. Following are the major types of registers:

    • Address Register

    • Instructions Register

    • Storage Register

    • Accumulator Register

Soft Copy

It displays the data on screen of monitor. It can be carried in a floppy disk. A change can be made in a soft copy.

Hard Copy

  • The data is printed on paper card etc. with the help of printer. It cannot be carried in a floppy disk. No change can be made in hard copy.