FOUR GENERATIONS OF COMPUTERS
The first vacuum tube computers are referred to as first generation computers, and the approximate period of their use was from 1950 to 1959. UNIVAC 1 (UNIVersal Automatic Computer) is an example of these computers which could perform thousands of calculations per second. Those devices were not only bulky, they were also unreliable. The thousands of vacuum tubes emitted large amounts of heat and burned out frequently.
The transistor, a smaller and more reliable successor to the vacuum tube, was invented in 1948. So-called second generation computers, which used large numbers of transistors, were able to reduce computational time from milliseconds to microseconds, or millionths of seconds. Second-generation computers were smaller, faster and more reliable than first-generation computers.
Advances in electronics technology continued, and microelectronics made it possible to reduce the size of transistors and integrate large numbers of circuit elements into very small chips of silicon. The computers that were designed to use integrated circuit technology were called third generation computers, and the approximate time span of these machines was from 1960 to 1979. They could perform many data processing operations in nanoseconds, which are billionths of seconds.
Fourth generation computers have now arrived, and the integrated circuits that are being developed have been greatly reduced in size. This is due to microminiaturization, which means that the circuits are much smaller than before; as many as 100 tiny circuits are placed now on a single chip. A chip is a square or rectangular piece of silicon, usually from 1/10 to 1/4 inch, upon which several layers of an integrated circuit are etched or imprinted, after which the circuit is encapsulated in plastic or metal.

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