An Analysis of Time-Shared Computer Systems

Abstract

Some of the aspects of the operation of time-shared, interactive computer systems are analyzed. The emphasis is on the reaction of hardware systems to the demands that its users make upon it. Simply shared systems and their users in order to be able to predict the performance of the two operating together. Portions of this problem include the specification and measurement of user characteristics, the development and verification of both simulation and mathematical models for time-shared systems, and the specification and measurement of performance metrics for such systems. The user and some of the performance measurements were made on Project MAC's "Compatible Time-Sharing System" (CTSS). First, simulation models are used to study the effects of changing small details in the operation of CTS-like systems. Then, a continuous-time Markov process model is derived to predict the performance of a broad class of systems. Throughout, the CTSS data are used as a basis for comparison with model predictions. In order to be able to take measurements and to build models, many definitions of commonly used time-shared system terminology are made precise.