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A computer is a programmable machine that receives input, stores and manipulates data, and provides output in a useful format. Although mechanical examples of computers have existed through much of recorded human history, the first electronic computers were developed in the mid-20th century (1940-1945). These were the size of a large room, consuming as much power as several hundred modern personal computers (PCs). Modern computers based on integrated circuits are millions to billions of times more capable than the early machines, and occupy a fraction of the space. Simple computers are small enough to fit into small pocket devices, and can be powered by a small battery. Personal computers in their various forms are icons of the Information Age and are what most people think of as "computers". However, the embedded computers found in many devices from MP3 players to fighter aircraft and from toys to industrial robots are the most numerous.

Earliest Computing Devices

1. Main frame computer- 1st generation

2. Mini computer- 2nd generation

3. Micro computer- 3 generation

4. Laptop & notebook- belongs in 3rd generation

5. Palm top computer- 4th generation


Fingers were man's earliest calculating device. By increasing or decreasing the number of fingers he displayed he was able to perform simple subtraction and addition. But finger counting has its limitations so man developed more sophisticated devices for counting.


The Quipu was the very first analog computer used by Incan tribes (ancient Indian civilization in North America). The computation was done by counting the number of knots.


The Abacus was the next analog computer which was developed in China in the 12th Century A.D. The device has a frame with its beads strung on wires or rods. Arithmetic calculations are performed by manipulating the beads. It was also known as Soroban in Japan and Suan Pan in China. To these days, old folks still use this device despite the presence of modern calculator especially at China Towns in different countries. The old folks are used to it compare to calculators.

Napier's Bones Napier's Bones is composed of eleven rods with numbers marked on them in such a way that by simply placing the rods side by side products and quotients - large numbers can be obtained. The sticks were called bones because it is made of bone or ivory. It was named after Scottish mathematician John Napier, who is famous for his invention of logarithms.

Classification of Computers

Super computer

The biggest in size, the most expensive in price than any other is classified and known as super computer. It can process trillions of instructions in seconds. This computer is not used as a PC in a home neither by a student in a college. Governments specially use this type of computer for their different calculations and heavy jobs. Different industries also use this huge computer for designing their products. In most of the Hollywood's movies it is used for animation purposes. This kind of computer is also helpful for forecasting weather reports worldwide.


Another giant in computers after the super computer is Mainframe, which can also process millions of instruction per second and capable of accessing billions of data. This computer is commonly used in big hospitals, air line reservations companies, and many other huge companies prefer mainframe because of its capability of retrieving data on a huge basis. This is normally to expensive and out of reach from a salary-based person who wants a computer for his home. This kind of computer can cost up to thousands of dollars.


This computer is next in he line but less offers less than mainframe in work and performance. These are the computers, which are mostly preferred by the small type of business personals, colleges, etc.

Personal computers

Almost all the computer users are familiar with the personal computers. They normally know what the personal computer is and what are its functions. This is the computer mostly preferred by the home users. These computers are lesser in cost than the computers given above and also, small in size; they are also called PCs in short for Personal computers. This computer is small in size and you can easily arrange it to fit in your single bedroom with its all accommodation. Today this is thought to be the most popular computer in all.

Notebook computers

Having a small size and low weight the notebook is easy to carry to anywhere. A student can take it with him/her to his/her school in his/her bag with his/her book. This is easy to carry around and preferred by students and business people to meet their assignments and other necessary tasks. The approach of this computer is also the same as the Personal computer. It can store the same amount of data and having a memory of the same size as that of a personal computer. One can say that it is the replacement of personal desktop computer.

FIRST GENERATION (1942 - 1955)

We have already discussed about some of the early computer - ENIAC, EDVAC, EDSAC, etc. These machines and other of their time were made possible by the invention of "vacuum tube", which was a fragile glass device that could control and amplify electronic signals. These vacuum tube computers are referred to as first-generation computers.


1. Vacuum tubes were the only electronic components available during those days.

2. Vacuum tube technology made possible the advent of electronic digital computers.

3. These computers were the fastest calculating devices of their time. They could perform computations in milliseconds.


1. Too bulky in size.

2. Unreliable.

3. Thousands of vacuum tubes that were used emitted large amount of heat and burnt out frequently

4. Air conditioning required.

5. Prone



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