Partial match retrieval in two-headed disks

Abstract

The performance of a disk with two heads per surface separated by a fixed number of cylinders is examined. We derive the probability distribution of arm stops, the expected number of stops as well as the expected number of cylinder clusters, i.e. the number of sets of consecutive compound cylinders. In comparison with a single-headed disk, it is shown that the performance gain may reach 50% on the average. 2 (b,a) (b,b) (b,c) (b,d) :2 Ca,b) (b,c) (c,d) (d,a) 3 (c,a) (c,b) (c,c) (c,d) 3 (a,c) (b,d)(c,a)(d,b) 4 (d,a) (d,b) (d,c)(d,d) 4 (a,d) (b,a) (c,b) (d,c)