Virtual machine systems have been implemented on a limited number of third generation computer systems, for example CP-67 on the IBM 360/67. The value of virtual machine techniques to ease the development of operating systems, to aid in program transferability, and to allow the concurrent running of disparate operating systems, test and diagnostic programs has been well recognized. However, from previous empirical studies, it is known that many third generation computer systems, e.g. the DEC PDP-10, cannot support a virtual machine system.

A review of computer systems simulation is presented. Existing and proposed programs for simulating computer systems are described and recommendations are made about the desirable characteristics of a simulator. Attention is primarily focused upon those simulators that may be used to study time-sharing, multiprogramming, and multiprocessing systems. It appears that a higher order, special purpose simulation language is needed for simulating computer systems. CSS and LOMUSS II seem to be representative of the most promising type of computer system simulators.