Initially , the term generation was used to distinguish between different hardware technologies. Nowadays , there are both generation hardware and software that together make a complete computer system. There are five computer generations known so far. Each generation has been discussed in detail along with their duration and characteristics. In the table below , the approximate dates are specified in each generation , which is generally accepted. First Generation - First Generation 1947-1959. Vacuum tube based. Second Generation - Second Generation: 1959-1975. Transistor based. Third Generation - Third Generation 1975-1981. Integrated circuit based. Fourth Generation - Fourth Generation: 1971-1980. VLSI microprocessor based. Fifth Generation - Fifth Generation: After 1960. ULSI microprocessor based