Operating Systems · Chapter 11

Disk Scheduling Simulator

Compare how different disk scheduling policies order cylinder requests and how much total head movement each policy requires.

Algorithm Initial head Max cylinder Direction

Request queue

Result

Total head movement–

Requests served–

Average seek distance–

Algorithm Comparison

Algorithm Guide

FCFS: serves requests in arrival order.

SSTF: serves the pending request closest to the current head position.

SCAN: moves like an elevator to one end of the disk, then reverses direction.

C-SCAN: serves in one direction only; after reaching one end, it jumps to the other end.

LOOK: like SCAN, but reverses at the last request rather than the physical disk boundary.

C-LOOK: like C-SCAN, but jumps between the last request on one side and the first request on the other side.

For SCAN and C-SCAN, travel to physical disk boundaries is counted as head movement. For LOOK and C-LOOK, only requested cylinders define the turning/jump points.