The 4th Generation of computers (~1971/1975 to ~1990) have a dedicated Central Processing Unit IC and almost exclusively use Integrated Circuits throughout their design. The CPU allows a large amount of complex circuitry to be contained within one chip, with the ALU, Buffers, Cache, Registers, memory control, look-up tables, power management and many other advanced features to be contained within a single IC chip. Before hand, this circuitry formed most of the size of a computer.
This allows the computers to be very small, some being built on a single circuit board, giving them the name of Microcomputer. You still get Mainframes, Supercomputers and Minicomputers, but it was the Microcomputer with its cheap price which really brought the computer to the home market.
Game Orientated Machines