We are living in Computer age. Most of our day-to-day jobs are being influenced by the use of computer. In some areas such as science and technology improvements cannot be achieved without the use of computer. Hence it has become necessary for each and every one of us to have a basic knowledge of computers.

Many people are aware that a computer is a machine that can perform arithmetic operations. But they fail to understand that it is also a machine that can choose, copy, move, compare and perform other non-arithmetic operations on many alphabetic, numeric and other symbols that we use to represent things.

The four characteristics of computers, which make them very useful tools, are speed, storage capacity, consistency and accuracy.

In addition to being fast, computers are also very accurate. However it has to be remembered that the computer is only capable of doing what it is instructed to do. Hence, errors may occur only due to inaccurate program ( a series of step-by-step instructions that provide a problem, solution and tells the computer exactly what to do) or data.


Unlike human beings, computers are very consistent and are not bored or tired when performing many thousands of calculations. They are ideal machines for carrying out works of a highly repetitive nature. They can also store large amounts of data. Once recorded, a piece of information can never be forgotten and can be retrieved within a fraction of a second.

The first computers were built to manipulate number in order to solve arithmetic problems. But soon computer scientists invented methods to manipulate symbols and data.

Computers are electronic devices that can store, transmit and manipulate data and information. To process data it requires instructions to be given. The instructions are input through an input device called keyboard, which is then processed, and the output is viewed on an output device such as a monitor.

Computers may be broadly classified into following categories:


1. Based on the operating principle

a) Analog Computers: – An Analog Computer basically sets up a model of the problem that is to be solved. They operate by measuring. Variations in voltage are used to represent different aspects of the problem.

b) Digital Computers: – In Digital Computers, the quantities are expressed as discrete digits or numbers. They are very useful for arithmetic expressions.

c) Hybrid Computers: – A Hybrid Computer is a combination of analog and digital types. The computers that are manufactured today are hybrid computers.


2. Based on the size

a) Super Computer: – It is mainly used for scientific purpose to perform large mathematical calculation. The first super computer was developed in India by CDAC (Center for Development and

Advanced Computing) called Param 2000. The biggest Super Computer Division in Asia is at IISc, Bangalore (Indian Institute of Science).

b) Mainframe Computer: – It is used to process large volume of data. Mainly used by commercial establishments such as banks and other financial organisations.


c) Mini Computers: – It is used to process medium volume of data. This can be used for networking (LAN and WAN).

d) Micro Computers: – Also called as personal computers. It is very widely used by individuals. It is used to process low volume of data. This can be used as a standalone computer and also in the network environment.

3. Based on the application

a) General Purpose Computers: – General purpose computers are those computers used for any commercial purpose such as banking, inventory, production, sales and marketing, etc.


b) Special Purpose Computers :- These machines are used for specific purpose such as launching of satellites, Weather forecasting, remote sensing etc.

Merits and demerits


1. Speed. The speed of carrying out the given instructions either numerical, logical or sorting is incomparable between a computer and a human being. A computer can carry out an instruction in less than millionth of a second. The speed of the computer is specified in terms of nanosecond and in picosecond.


2. Storage: A man’s brain can store a piece of information to some limitation of numbers and up to some extent of time only. Computer can store more data internally as well as externally.

3. Accuracy: Computer calculates accurately, but we often hear about false results of a computer. The computers never do mistakes. The mistake of the human data entry operations and poorly designed programs only lead to a computer output, which provides incorrect results.

4. Automaticity: A computer performs automatically particularly in user friendly and menu driven programs. Electronic equipments like tape recorder, television, VCR, calculator etc, can be operated just with a knowledge of their basic operations. In the same way with some basic know-how techniques computer can be operated.

5. Versatality : It is versatile. The computer was so far mistakenly understood as a calculating machine only. But, it can also carry out logical operations. Any job can be computerised with appropriate software. A limited set of instructions are enough to carry out a computer processing.

6. Compactness’. The present day computers are table top computers, which do not occupy much space. Moreover the personal computers need only dust free room and so air conditioning expenditure is avoided.

7. Reliability: Computers have long life if maintained properly, the latest microprocessors are guaranteed for several years.

8. Repetitiveness: A computer can be used repetitively to process information. It will not get mental fatigue as seen in the case of the human beings or will not lose its speed.

9. Diligence: A computer does not suffer from human traits of lack of concentration, so the results will be continuously of the same standard.


1. Common sense lacking: Computer is only a tool, it cannot think. If we provide an incorrect data, it will not have the common sense to question the correctness of the data.

2. Memory without brain: Computer can store data in its memory but if a wrong data or instructions is provided it dose not have a brain to correct it.

3. Slavery : A computer is a slave, unless instructed by itself, it cannot generate any information.

4. Costly : – Computers in rural India is still a luxury. People are not able to afford a personal computer.

5. Hacking: There is a threat for the personal computer that is used. It could be attacked with viruses that can affect data residing in the system. It is difficult to guard data against different kinds of attacks.