Generations of Computer.

First-generation computers, starting with the UNIVAC I in 1951, used vacuum tubes, and their memories were made of thin tubes of liquid mercury and magnetic drums.
Second-generation systems in the late 1950s replaced tubes with transistors and used magnetic cores for memories (IBM 1401, Honeywell 800). Size was reduced and reliability was significantly improved.
Third-generation computers, beginning in the mid-1960s, used the first integrated circuits (IBM 360, CDC 6400) and the first operating systems and DBMSs. Online systems were widely developed, although most processing was still batch oriented using punch cards and magnetic tapes.
Starting in the mid-1970s, the fourth generation brought us computers made entirely of chips. It spawned the microprocessor and personal computer. It introduced distributed processing and office automation. Query languages, report writers and spreadsheets put large numbers of people in touch with the computer for the first time. Even with the hundreds of millions of people using computers every day, we are still in the fourth generation. Some skill is still required to use the computer even if only to surf the Web and send e-mail.