Computer is an electronic machine and a mechanical device which can store, retrieve and manipulate the ‘data’ with high speed and accuracy according to a list of instructions called ‘programmes’.

It is a device that processes the data. Due to technological advancement, modern electronic computers are exponentially more capable than those of preceding generations. However, it does the following function during data processing.

(i) It accepts the data from the users called ‘input’.

(ii) It accepts instructions from the users input’.


(iii) It converts the data into information ‘processing’.

(iv) It displays the results as ‘output’.

It means that a computer performs all the work in an integrated way.

Input Unit ->Processing Unit -> Output Unit


1. History of Computers :

In 1801, Joseph M. Jacquard used a series of punched paper cards as a programme to weave intricate patterns. The resulting Jacquard loom is not considered a true computer but it was an important step in the development of modern digital computers.

Babbage first conceptualized and designed a fully programmable computer as early as 1820. By the end of the 19th century several technologies had appeared such as the punch card and the vacuum tube. Large-scale automated data processing using punch cards was performed by tabulating machines designed by Hermann Hollerith.

During the first half of the 20th century, many scientific computing needs were fulfilled by sophisticated special-purpose analog computers. A direct mechanical or electrical model of the problem was used as a basis for computation.


In the 1930s and 1940s, a succession of steadily more powerful and flexible computing devices were constructed gradually adding the key features of modern computers, such as the use of digital electronics and more flexible programmability.

Notable achievements include a special-purpose machine that used valve-driven (vacuum tube) computation, binary numbers, and regenerative memory. The decimal-based American ENIAC (electronic numeric integrator and calculator) computer (1946) was the first general purpose electronic computer.

Originally it had an inflexible architecture that meant reprogramming it required was to be rewired. This stored programme architecture became the basis for virtually all modern computers. In the mid to late 1940s, a number of projects to develop computers based on the stored programme architecture were started.

During 1950s, valve (tube) driven computer designs were in use. But it were eventually replaced with transistor-based computers. These were smaller, faster, cheaper and much more reliable which allowed them to be commercially produced in the 1960s.


By 1970s, the adoption of integrated circuit technology had enabled computers to be produced at a low cost to allow individuals to own a personal computer (PC).

2. Classification of Computers:

There are different types of inputs that computers accept. On this basis, computers can be classified into three types: analog computer, digital computer and hybrid computer.

(a) Analog Computer:


The computers that use signals as input are called analog computers. The signals are the temperature, pressure, speed, etc. Signals flow continuously in these computers. However, signals can also be fed in these computers for the purpose of processing. The examples of analog computers are thermometer, speedometer, etc.

(b) Digital Computers:

Digital computers accept digits and alphabets as inputs; therefore, these are called digital computers. For example, computers used in business purpose are digital computers because data are inserted in the form of digits and alphabets.

(c) Hybrid Computers:


Variations are found in methods of applications. If you want to observe the variation in signals, it becomes rather difficult. Because variations in signals are very small that is why these cannot be checked manually.

But the action is to be taken very fast. It makes impossible for a man to act within the required time. Now it can be done by hybrid computers which deal with such applications.

Hybrid computers require two types of inputs: (i) signals of which variations are to be monitored, and (ii) instructions for monitoring and doing the actions. Instructions are in the form of digits and alphabets. Therefore, hybrid computers use signals, digits and alphabets as input.

For example, levels of radioactivity in an atomic reactor are measured by a computer. A hybrid computer needs the level of radioactivity as input i.e. signal. In computer instructions are given in the form of digits and alphabets the basic arithmetic and logical operation in the memory. Thus, they are very versatile in performing the functions.

(v) Automatic Work:

Overall, a computer is a machine. There is a need of an operator who feeds data in computer. It will process the data automatically and continuously as per instruction present in its memory, without human interference, and will provide the result.

(vi) A Diligent Machine:

A computer is very helpful to use. It never gets tired and never loses its concentration. If it has to do 15 million calculations, it will do the last function in the same speed and accuracy as the first function.