Microprocessors

Abstract

A microprocessor is a complete central processor on a single integrated circuit. From a computer scientist’s point of view, it is distinguishable from other types of computer only by its extremely low price and high reliability. It is sometimes said that microprocessors are ‘less powerful’ or ‘less versatile’ than minicomputers and main-frames. It is true that the first microprocessors to be offered for sale did have clumsy and inadequate instruction codes, and were handicapped by very short word lengths (such as 4 bits). At that time the number of gates which could be etched on to one chip of silicon was still severely limited, and the uncomfortable architecture of the first microprocessors resulted from the need to ‘shoehorn’ the design into this limit. Recently, the technology of chip production has improved and these restrictions no longer apply. Modern microprocessors have excellent order codes and for certain tasks are effectively just as fast as many minicomputers and main-frames. Some of them incorporate immediate access stores and peripheral control circuitry as well as a CPU, and this variety is said to be a complete ‘computer on a chip’. Others include all the mechanisms for giving efficient support to high-level languages, and for controlling very large stores. There is a tendency among manufacturers to put microprocessors into sealed boxes and to market the result as ‘main-frames’. The microprocessor is chosen with the same order code as the machine to be replaced, so that the software can be transferred directly.