Explanation

Vacuum tubes as the basic components for memory and circuitry for CPU .

These tubes, like electric bulbs, produced a lot of heat and the installations used to fuse frequently.

First generation (1940 - 1956) vacuum tubes as a major piece of technology. 

The ENIAC is  example of 1st generation computer.

Second generation (1956 - 1963) use of transistors.

Third generation (1964 - 1971)  use of Integrated circuits.

Fourth generation (1972 - 2010) use of the microprocessor.

Fifth generation (2010 to present) use Artificial intelligence.