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+12 votes

Consider a disk system with 100 cylinders. The requests to access the cylinders occur in 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 1ms to move from one cylinder to adjacent one and shortest seek time first policy is used?

- 95 ms
- 119 ms
- 233 ms
- 276 ms

+14 votes

Here in case of Shortest seek time first we don't need to do lot of substraction & addition in this type of questions. It seems like it is necessary to actually calculate small differences ! It is better to just draw actual movement & Then do computation.

Here sequence is like

50->34->20->19->15->7->4->2->73

So we can calculate like (50-2) + (73-2) = 71+48 = 119.

Here sequence is like

50->34->20->19->15->7->4->2->73

So we can calculate like (50-2) + (73-2) = 71+48 = 119.

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