We live in an age of science. We can see the wonders of science around us. Science has mad our life easy and comfortable we can't thing of our modern life with out science.
The first wonder of modern science is the discovery of Electricity.
It has changed our life, society, and culture .It is a great source of power and energy.
The radio, television, lights, fans, electronic iron, mills,factories and refrigerators all work though the power of electricity.
Science has invented many wonderful thing and computer is one of them. It is the most wonderful invention of modern science.
Computer:
The word computer is derived from the Latin word "computaer", which means a calculating machine. It was first used as a counting machine. Recently its uses and importance are seen dominating almost in the whole of our working fields. Computer is an ultra-modern electronic device. which accepts data through input device, stores and processes mathematically or logically and then sends the result through the output device according to the user requirements. It work on the given instruction of human being.
Computer Generation:
Computer can not come to its present stage by one step. It has to go through many steps. In keeping with the improvement of electronics industries computer has also been improved. In 1951 first electronics computer UNIVAC ( Universal Automatic Computer ) was invent by heart and soul trying of some mathematicians. The age from 1951 even today can be divided into some generations. They are as follows.
(a) First Generation: From 1951 which computers are introduced as first generation computer. A main feature of first generation computer is to utilize tubes in their electronics circuits. Because of using huge numbers of vacuum tube a computer looked big in structure and needed more electricity.
(b) Second Generation: from 1959 to 1965 which computers are introduced as the second generation computer. Main feature of second-generation computer were the using of transistors in the place of vacuum tubes. Because of using transistors second generation computers become in small structure and needed lower cost of electricity.
(c) Third Generation: From 1966 to 1970 which computers are introduced as third generation computers. Into those computers I.C. (Integrated circuit) were used.For using I.C. these computer become too small in structure and working efficiency was also upgraded. There are many Diodes, Transistors and other electronic parts in to an I.C. chip. More high level languages were used in third generation computers and its using also easy and simple.
(d) Fourth Generation: From 1971 to 1995 which computers are introduced are called fourth generation computers. This computers were produced with Large Scale Integration (LSI) and very large Scale Integration (VLSI) Microprocessors and semi conductor memory. As a result these computers were with high speed, high programming Language 'PASCAL' etc was the contributions of this generation.
(e) Fifth Generation: In 1981 at Japan 300 computer scientists and engineers of 14 countries declared as fifth generation computer, which would be produced after 1995. At that time scientists thought that fifth generation computers would be able to understand human language and according to those order or language they (computer) would be able to perform special task. This is why fifth generation computer would be enriched with artificial wit or brain. Type of Computers: On basis of structure, computer are classified in three type as-
1- Digital Computer.
2- Analog Computer.
3- Hybrid Computer.
Digital Computer: A
majority of the computers used in the world today are digital.A digital
computer processes information which is based on the absence or
presence of an electric plus, an on (1)/ off (0) condition. So a
computer that counts the numbers and works directly on digits that
represent either discrete data or symbols is called digital computer.
These types of computers are able to give acute and error less result.
Analog Computer: A
computer that can measure continuous physical quantities such as
electrical current, length, temperature, pressure, shaft rotations,
voltage etc. and convert them to analogous decimal digits, and them
realizes an arithmetic or logical operation and accomplished result is
visible by meter or indicator is called analog computer, Speedometer of
motorcar, thermometer etc. are ideal examples of analog machine. Analog
computers are used mainly for scientific and engineering purposes
because they deal with quantities that very constantly. These type of
computers give approximate result only.
Hybrid computer: The
best combination of digital and analog computer is called hybrid
computer. The hybrid computer takes analog inputs, converts them into
digital data and processes them in digital form. Whether the output is
digital or analog is a matter of requirement. These types of computers
are used in real-time processing like whether forecasting and in the
intensive care of a Hospital.
Classification of Computers:
Computers are available in different size with different capabilities. They may be classified in the following four categories.
1- Super Computer.
2- Mainframe Computer,
3- Mini Computer.
4- Micro or Personal Computer (PC).
Super Computer: Super computer is the most powerful, expensive, and high speedy computer. In a few countries of recent world have super computer. It can perform more than crores of calculation within a second. This computer is being used sophisticated scientific research, cosmic research, and in the military affairs. Its sale and production are restricted.
Mainframe Computer: Mainframe computer is less powerful than the super computer than can analyses huge quickly. They are used in big research institutes, education institutes, banks, large organizations etc. A large number of users can use such a computer simultaneously. 
Mini Computer: A physically small and less working capability computer compared to mainframe is called mini computer. This type of computer can be set up in a large size table. Many users can use it simultaneously by connecting several terminals. Mini computer is generally used in Office, Banks, Clinics, Hospitals, Garments factory and multinational companies etc. The PDP Series of computers are mini computers.
Micro or Personal Computer(PC): In November, 1977 Intel company at first produced Microprocessor. This Microprocessor is introduced as Intel-4004, which is mainly used in calculator. The word Micro means very small. That is why a microcomputer made with mini microprocessor is called Microcomputer. Only one can use this type of computer at a time, so it is called Personal Computer (PC). A man in general stage could be able to use computer technology when the microcomputer came broad way. Besides in official works computer is being used extensively in home-works, sports, and recreations and in personal affairs. Microcomputer is mainly contained unique processor. Recently multiprocessor is being built with microcomputer. The working official processor used in Microcomputer is going to the way of development is so torrent that meanwhile the necessity of minicomputer is being mitigated by microcomputer. A few dates ago men could only think to used microcomputer setting on a desktop. At present it is also found in the shape of briefcase and mini books. 