QUEUEING MODELS FOR FILE MEMORY OPERATION

A model for the auxiliary memory function of a segmented, multiprocessor, time-shared computer system is set up. A drum system in particular is discussed, although no loss of generality is implied by limiting the discussion to drums. Particular attention is given to the queue of requests waiting for drum use. It is shown that a shortest access time first queue discipline is the most efficient, with the access time being defined as the time required for the drum to be positioned, and is measured from the finish of service of the last request to the beginning of the data transfer for the present request. A detailed study of the shortest access time queue is made, giving the minimum access time probability distribution, equations for the number in the queue, and equations for the wait in the queue. Simulations were used to verify these equations; the results are discussed. Finally, a general Markov Model for Queues is discussed in an Appendix.