An approach is presented to analyzing and controlling hardware and software configurations of a time-sharing system given its load characteristics and desired performance. A mathematical model is developed which predicts response time to both interactive terminal requests and to compute bound programs. Estimates are obtained which relate performance to CPU load, file I/O load, and swap I/O load. Instrumentation contained within the UTS time-sharing system measures actual load and actual response during system operation, These measures suggest standards by which both load and response of time-shared systems could be compared, Extrapolation of the modeled and measured results allows prediction of performance for a variety of hardware configurations and user loads. Administrative controls allow dynamic tuning of the system during actual operation utilizing displays of current performance.