Consider a disk system with cylinders. The request to access the cylinders…
2023
Consider a disk system with cylinders. The request to access the cylinders occurs 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?
Answer: A. 119 ms — Under SSTF, always choose the pending request nearest to the current head position. Starting at 50, the service order is 50 -> 34 -> 20 -> 19 -> 15 -> 10 -> 7…
- A.
119 ms
- B.
120 ms
- C.
142 ms
- D.
146 ms
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Correct answer: A
Under SSTF, always choose the pending request nearest to the current head position. Starting at 50, the service order is 50 -> 34 -> 20 -> 19 -> 15 -> 10 -> 7 -> 6 -> 4 -> 2 -> 73. Total head movement = 16 + 14 + 1 + 4 + 5 + 3 + 1 + 2 + 2 + 71 = 119 cylinders. Since each adjacent-cylinder move takes 1 ms, total time = 119 ms.
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