This paper describes the use of simulation techniques at SDC in the analysis of time-sharing system operation. The purpose and goals of this research effort are briefly outlined and some comments on the advantages and disadvantages of direct simulation for this type of work are given. The existing simulator models are described in terms of inputs, general flow, and outputs; and the results of initial investigations with these models are given. Work currently in progress is discussed, and some related problems that may possibly be studied in the future by similar methods are noted.