GATE - 2014 | OS | Suppose a disk has 201 cylinders, numbered from 0 to 200. At some

GATE - 2014 | OS | Suppose a disk has 201 cylinders, numbered from 0 to 200. At some
Posted on 10-02-2022

GATE - 2014 [Operating System]

Question:

Suppose a disk has 201 cylinders, numbered from 0 to 200. At some time the disk arm is at cylinder 100, and there is a queue of disk access requests for cylinders 30, 85, 90, 100, 105, 110, 135 and 145. If Shortest-Seek Time First (SSTF) is being used for scheduling the disk access, the request for cylinder 90 is serviced after servicing ____________ number of requests.

A

3

B

4

C

5

D

6

    

Solution:

Option (A) is Correct.

Suppose a disk has 201 cylinders, numbered from 0 to 200. At some time the disk arm is at cylinder 100, and there is a queue of disk access requests for cylinders 30, 85, 90, 100, 105, 110, 135 and 145. If Shortest-Seek Time First (SSTF) is being used for scheduling the disk access, the request for cylinder 90 is serviced after servicing ____________ number of requests.

90 is serviced after servicing three requests, i.e.,
100 → 105 → 110 → 90

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