Disk requests come to a disk driver for cylinders in the order 10, 22, 20, 2,…
2018
Disk requests come to a disk driver for cylinders in the order 10, 22, 20, 2, 40, 6, and 38 at a time when the disk drive is reading from cylinder 20. The seek time is 6 ms/cylinder. The total seek time, if the disk arm scheduling algorithms is first-come-first-served is
- A.
360 ms
- B.
850 ms
- C.
900 ms
- D.
None of the above
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Correct answer: D
1. Initial head position: Cylinder 20. 2. Request sequence: 10, 22, 20, 2, 40, 6, 38.
3. Calculate seek distance for each move: - 20 to 10: |20-10| = 10 - 10 to 22: |10-22| = 12 - 22 to 20: |22-20| = 2 - 20 to 2: |20-2| = 18 - 2 to 40: |2-40| = 38 - 40 to 6: |40-6| = 34 - 6 to 38: |6-38| = 32
4. Total seek distance = 10 + 12 + 2 + 18 + 38 + 34 + 32 = 146 cylinders. 5. Total seek time = 146 * 6 ms = 876 ms.
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