1410	 Interarrival Statistics for Time Sharing Systems	 The optimization of time-shared system performance requires the description of the stochastic processes governing the user inputs and the program activity. This paper provides a statistical description of the user input process in the SDC-ARPA general-purpose Time-Sharing System TSS . The input process is assumed to be stationary and to be defined by the interarrival time distribution. The data obtained appear to justify satisfactorily the common assumption that the interarrival times are serially independent. The data do not appear to justify except as a very rough approximation the usual assumption off an exponential distribution for interarrival time. A much more satisfactory approximation to the data can be obtained with a biphase or triphase hyperexponential distribution.
