1. First Generation Computers (1940-1956)
The first generation computers were employed during the period 1940-1956. These computers used the vacuum tubes technology for calculation as well as for storage and control purposes. Therefore, these computers were also known as vacuum tubes or thermionic valves based machines. A vacuum tube is made up of glass and contains filaments inside it. The filaments when heated generate electrons, which eventually help in the amplification of electronic signals. The input and output medium for first generation computers was the punched card and printout, respectively. Some examples of first generation computers are EN IAC, ED VAC, EDS Ac and UNIVAC.
2. Second Generation Computers (1956-1963)
The second generation computers were employed during the period 1956-1963. The main characteristics of these computers were the use of transistors in the place of vacuum tubes in building the basic logic circuits. The transistors were invented by Shockley, Brattain and Bardeen in 1947 for which they won the Nobel Prize. A transistor is a semiconductor device that is used to increase the power of the incoming signals by preserving the shape of original shape. It has three connections, which are emitter, base and collector. The base of the transistor is the gate through which the signal, needed to be amplified, is sent. The signal sent through the base of the transistor is generally a small flow of electrons. Therefore, the base terminal also acts as the input gate for the transistor. The collector of the transistor is used to collect the amplified signal. The emitter of the transistors acts as the output gate for emitting the amplified signal to the external environment. The transistor was far superior to vacuum tube that made computers become smaller, faster, cheaper, more energy efficient and more reliable than the first generation computers. Example : IBM 1401, UNIVAC-II, IBM 1620.
3. Third Generation Computer (1964-1971)
The third generation computers were employed during the period 1964-1971. The major characteristics feature of third generation computer systems was the use of Integrated Circuits (IC). The IC technology was also known as microelectronics technology. IC are the circuits that combine various electronic components, such as transistors, resistors, capacitors, etc. onto a single's mall silicon chip. This development made computer smaller, reliable and efficient. In this generation remote processing, time-sharing, multiprogramming operating system were used. The first IC was developed by Jack Kilby and Robert Noyce in the year 1958. Example: IBM 360, PDP-8, CDC 7600, NCR 395, B6500 etc.
4. Fourth Generation Computers (1971-present)
The fourth generation computers were employed during 1971. The invention of Large-Scale Integration (LSI) technology and Very Large-Scale Integration (VLSI) technology led to the development of fourth generation computers. However, these computers still used the IC technology to build the basic circuits. The LSI technology allowed thousands of transistors to be fitted onto one small silicon chip. On the other hand, the VLSI technology allowed hundreds of thousands of transistors to be fitted onto a single chip. As a result, the manufacturers were able to reduce the size of the computers and made them cheaper than compared to the other generation of computers. With the help of VLSI technology, microprocessor came into existence.
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