Combining RISC and CISC in PC systems

RISC processors are being increasingly used in computers in which performance is a key feature. However, their take-up may be restricted by the limited availability of software compared to that available for established machines, normally based on CISC processors. The paper describes a method in which RISC and CISC processors have been combined into the same machine in order to offer compatibility with a wide software base (that of the PC) and, at the same time, access to state-of-the-art computing performance. The hardware and software issues involved and the level of integration which can be achieved are also considered