2375	 A Comparative Analysis of Disk Scheduling Policies	 Five well-known scheduling policies for movable head disks are compared using the performance criteria of expected seek time system oriented and expected waiting time individual I O request oriented . Both analytical and simulation results are obtained. The variance of waiting time is introduced as another meaningful measure of performance showing possible discrimination against individual requests. Then the choice of a utility function to measure total performance including system oriented and individual request oriented measures is described. Such a function allows one to differentiate among the scheduling policies over a wide range of input loading conditions. The selection and implementation of a maximum performance two-policy algorithm are discussed. access time analytical models auxiliary storage direct access storage disk analysis disk scheduling performance criteria peripheral memory devices real-time systems response time rotational delay scheduling policies seek time simulation storage units time-sharing systems waiting time
