Disk scheduling in System V

Abstract
A variety of disk scheduling algorithms, including some newly defined ones, are compared both in simulation and in tests on a real machine running UNIX * System V. In the real system tests, first-come first-served (FCFS), shortest seek time first (SSTF), and the standard System V algorithm (SVS) are all seen to yield relatively poor mean waiting time performance when compared to the VSCAN(0.2) algorithm and modifications thereof suggested by Coffman. Nevertheless, each is seen to excel along a particular performance dimension. The adequacy of open, Poisson arrival simulation models in predicting disk scheduling performance is questioned, and an alternative arrival model is suggested which offers improved predictions in the System V environment.

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