Project ForgeOperating Systems
Disk Scheduling & Geometry
GATE 2009
Hard
Consider a disk system with 100 cylinders. The requests to access the cylinders occur in the following sequence: 4, 34, 10, 7, 19, 73, 2, 15, 6, 20. Assuming that the head is currently at cylinder 50, what is the time taken to satisfy all requests if it takes 1 ms to move from one cylinder to adjacent one and shortest seek time first policy is used?
119 ms
Explanation
SSTF always services the nearest pending request: 50→34(16)→20(14)→19(1)→15(4)→10(5)→7(3)→6(1)→4(2)→2(2)→73(71). Total = 16+14+1+4+5+3+1+2+2+71 = 119 ms.
Source: GATE CS 2009 (2009)
This question is part of a 15-day revision cycle — sign in and Project Forge will bring it back the day before you'd forget it.