A computer receives incoming data, processes them and produces an output.

Hence, in a typical computer, there is

(a) An input device i.e., a key board

(b) A Central Processing Unit (CPU) i.e., a box and


(c) An output device i.e., a monitor or a Visual Display Unit (VDU)

(a) Input Devices

The most commonly used input device is a key board. It is just like a type-writer keyboard. Other types of input devices are Bar-Code Recognition, Hard-Held Terminal, and Hard Print Terminal or also called data tablet, Optical Mark Reading, Magnetic Ink Character Recognition (MICR), Optical Character Reader (OCR) etc.

(b) Central Processing Unit (CPU)


It has a box like appearance and is considered as the heart of the computer. It is consisted of;

(i) Control Unit (CU)

(ii) Arithmetic and Logic Unit (ALU) and

(iii) Primary Storage Unit, (i) Control Unit (CU)


The control Unit organizes all the operations. It selects, interprets and executes the programme instructions, (ii) Arithmetic and Logic Unit (ALU)

It does all the arithmetic and logic operations i.e., adding, subtracting, multiplying, dividing and comparing, (iii) Primary Storage Unit

It is the memory section of CPU that stores data and programmes that are waiting to be processed or currently being processed.

Generally two different types of memory are used in the computers; i.e.


(1) Random Access Memory (RAM), and

(2) Read Only Memory (ROM)


It allows read/write but is volatile i.e., loses Memory when power is cut.



It is non-volatile and is put in by the manufacturer. It is commonly used not storing of programme instructions that are not subject to change. There are various ROM chips to meet user’s specifications; like

PROM Programme Read Only Memory

EPROM Erasable Programme Read Only Memory


EEROM Electrically Erasable Read Only Memory

All the information’s within the computer is stored in the form a BINARY SYSTEM i.e.. O’s and 1’s.

(c) Output Devices:

Output devices communicate the result to the users. They are

(i) Visual Display Unit (VDU)

(ii) Printers

(iii) Plotters

(i) VDU: It is like a T. V. screen or a monitor where all data can be displayed.

(ii) Printers: The printers are devices that can be reproduced on papers, copies of programs, data or output from the computer’s memory. Different kinds of printers are, Dot Matrix. Thermal, Ink Jet, Daisy wheel, Thimble, Spark, Drum, Chain and Laser printer.

In Dot-matrix, characters are made up of patterns of dots. Dot-Matrix image with overlapping dots gives rise to Laser Printer. In Page Printer, one page is printed at a time, (iii) Plotters: A plotter is a device used to draw graphs, diagrams or any other drawings on the paper.

Secondary Storage Devices

All devices that are connected to the CPU for storing information’s but are not part of the CPU, are called Secondary Storage Devices. The examples are; Magnetic Tap, magnetic disk. Optical disk, Winchester or Hard disk and Floppy disk.

Floppy disk

Floppy disks or diskettes are most widely used in microcomputers and are very popular. These are thin, plastic disks on which computer data and programmes can be stored. The sizes may very from 3.5″ to 5.25″ to 8″ and have large storage capacity. The information can be stored on the floppy either on one side, i.e., single-sided (ss) or in both sides i.e., double-sided (do) and in single density (sad) or double density (did) or high density (had).

Winchester disk or Hard disk

These are IBM innovation and can store much more data that can be stored in floppy disk and have more reliability. Hard disks usually come as sealed units. So they can not be removed or changed like floppy disk and cost is also 2-10 times more than floppies. But they have greater protection and do not need periodic maintenance.

Hardware and Software

Computer ware can be divided into two types e.g. hardware and software.


All electronic, mechanical, magnetic, electrical and other devices used with the computer constitute the hardware.


Software refers to various Programs or routines used on the hardware to facilitate the user’s efficient operation of the computer. The software can be divided into two kinds; System software used to manage the operations of the machine i.e., the Operating Systems (OS) and Application software’s are used for the user applications i.e., a programme that is employed for data bases for railway enquiry or reservation system or airlines booking etc..

The Operating System (OS)

The Operating System (OS) of a computer is a set of specialized programmes that manages all the operations of the computer; such as CPU, Memory, key board, Floppy Disks, VDU etc. The Operating System is responsible for the communications between the computer and its peripheral. From small personal computer (Micro Computer) to super computers, the OS operates in all the computer systems. Very commonly used operating systems for microcomputers are PC-DOS (Personal Computer Disk Operating System), MS-DOS, Window and XENIX. IBM’s PC-DOS is a very popular OS. UNIX another very powerful OS is much more versatile and also offered many more capabilities than any other OS.

Program and programming language

A Program is a sequenced set instruction to a computer to do a particular job and the art of writing a program is called programming. A language is used by programmers to write computer programs and routines and is called programming language.

In a binary-coded digital computer, Os and Is are used as low level language called machine language. But for better use, several hundreds of easier high level programming languages like FORTRAN (Formula Translation), ALGOL (ALG Orithmic Language) BASIC (Beginners All Purpose Symbolic Instruction Code). COBOL (Common Business Oriented Language) PASCAL and C etc. are developed.

Among them, BASIC is the most fundamental and commonly used language whereas COBOL is mostly used in business application. C is the latest development. All these are third generation languages. But there are also the fourth generation languages, like ORACLE, INGRESS etc.

Computer can understand two types of programming languages i.e. either compiled or interpreted languages. The high level programming languages used by users are called Source Code. But the machine can not understand these.

Hence these languages are being translated into a machine language program called object code. The translation jobs are done by translators which are actually the compilers. The source code program is being translated by the compiler to object code for execution of next stage operation.

Source – Translator – Object code

Thus in a compiled language, to run the program, two phases are there i.e., the compilation phase and the execution phase.

But in an interpreted language, on the other hand, the source program is directly translated line by line into machine language instructions for execution of any program. BASIC language on a micro computer is an interpreted language. Actually the manufacturer of the computer supplies the required software; either a compiler or an interpreter. But in latter case, it is easier to develop a program using this language.