Historians tell us that in ancient times the usual mode of operation of a Computer System Manufacturer was for an electronic engineer to emerge from his laboratory one day and tell the waiting programmer "Look! Here's our next model!" The engineer then disappeared to work on the next-but-one model, leaving the programmer to work around any deficiencies or awkwardness in the hardware design which had been handed to him. In modern times, the idea that a machine should be designed to fulfil a function, that the intended use of the machine should supply constraints on its design (rather than the converse), has received at least lip service in most quarters. Some manufacturers have even adopted it as a way of life.