The first computer generation appeared in 1946-1958. It is the era of vacuum tubes. The computers of this era were huge, very expensive, slow and had limited application capabilities. The first computer that had vacuum tubes was constructed in 1946 by J. P. Eckert and J. Mauchly. Their machine was called ENIAC (Electronic Numerical Integrator and Computer). ENIAC had thousands of vacuum tubes.
The Second Generation: Transistors
The second generation of computers lasted from 1959-1964. It was a very short era. The vacuum tubes were replaced by transistors. Actually, the invention of a transistor had a huge influence on the development of electronics.
The invention of transistor allowed computer to become smaller, faster and cheaper. These computer also were more efficient and more reliable that the computers of the first generation. The first symbolic (assembly) programming languages appeared in this generation. Also, the backgrounds of high level programming languages were developed. The first versions of COBOL and FORTRAN appeared. The computer instructions storage also changed. The step from magnetic drum to magnetic core technology was made.
The Third Generation: Integrated Circuits
The invention of integrated circuits was another great step in developing semiconductor technologies. The third computer generation appeared. The third generation lasted from 1964 to 1971. The appearance of integrated circuits allowed placing miniaturized transistors on silicon chips. This technological invention allowed computers to increase speed and to become more efficient.
The human interaction with the computer had changed much in this generation. The keyboards and monitors appeared instead of punched cards and printouts. In this generation computers had first operating systems that allowed running multiple applications on the computer. It was the first time when computer became accessible to a mass audience. They become much smaller and cheaper, so the usual customer could afford them.