In the 1930's the predecessors of the computer were constructed from mechanical switches and relays. These were comparatively slow, large, and produced a great deal of heat. The next stage in the 1940's was the use of electronic diodes, and while these were better they were unreliable. The next stage was the result of the development in 1947 of the transistor which was much smaller, faster and cooler. Simple transistors were eventually replaced by integrated circuits (ICs) where the discrete circuit and transistors were engraved on boards that got smaller and smaller, and finally deposited on silicon to be put into a "chip". The "computer on a chip" was invented in about 1970.

In the USA:
George Stibitz Built the first adder about 1937	Jack St. Clair Kilby Invented the Integrated Circuit about 1960	Ted Hoff Built the first "computer on a chip" about 1970