The achievement of the microelectronics industry in integrating the components of a computer on to a few, or even a single, increasingly complex silicon chip has resulted in a reduction in price of the basic elements of a computer system by more than one hundred times. This technology has brought the cheap calculator which can now provide quite sophisticated programming functions that could only have been obtained with a computer occupying an equipment rack some few yean ago. The microprocessor is the most complex of the family of integrated circuits but its operation is not fundamentally different from that of its much larger predecessors, being a feat of technology rather than a new departure in computer design. It is the dramatic change in price and physical size, coupled with other associated technical advances such as low power consumption and reliability, that has made it possible for the use of computers to be considered in situations which could not reasonably be contemplated previously.

Although computers include those that operate or continuous, or analogue, variables, the predominanl interest is in digital systems. These operate on discrete values of electrical signals that represent, in coded forms, data or the operations to be performed. These operations can be arithmetical or logical and may be combined into a sequence that constitutes a program. The notion of stored program control, where such a sequence is held in the memory of the machine, provides the essential feature of computer operation.