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Operating systems miscellaneous

  1. 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 requests, if it takes 1 ms to move from one cylinder to adjacent one and shortest seek time first policy is used?
    1. 95 ms
    2. 119 ms
    3. 233 ms
    4. 276 ms
Correct Option: B

Requests 4 34 10 7
19 73 2 15 6 20
Current 50 34 20 19
15 10 7 6 4 2
Next access 34 20 19 15
10 7 6 4 2 73
Difference 16 14 1 4
5 3 1 22 71

Therefore, total moves = 16 + 14 + 1 + 4 + 5 + 3 + 1 + 2 + 2 + 71 = 119 ms



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