Queries on two headed fast disks with smart track management using dynamic scans

Abstract

Scan policies for two-headed disks using dynamic queues are simulated. Older format and latest format disks with one and two heads are compared. The results confirm a recent finding that the optimal head separation distance is about 0.47 N ( N is the number of logical cylinders on the disk), rather than [ N 2 ]. The maximum batch size need be no greater than 50 requests. Two heads are shown to reduce average service time by more than a third. Using cache memory to manage the accessing of sectors out of track sequence (smart tracking) reduces average service time for longer (near full track) requests by more than a third.