Practice mode Operating Systems

A disk has cylinders 0 to 199. The head is at cylinder 70 and the request queue is 120, 35, 180, 10, 95, 150, 60. What is the total head movement under SSTF scheduling?

Correct answer B. 230 cylinders

Explanation

SSTF always serves the closest pending request: from 70 it goes to 60 (10), 35 (25), 10 (25), then 95 (85), 120 (25), 150 (30) and 180 (30), a total of 230 cylinders. SSTF greatly reduces seek time, but like SJF it can starve requests far from the head while new requests keep arriving nearby.

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A disk has cylinders 0 to 199. The head is at cylinder 70 and the request queue is 120, 35, 180, 10, 95, 150, 60. What is the total head movement under SSTF scheduling?

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A disk has cylinders 0 to 199. The head is at cylinder 70 and the request queue is 120, 35, 180, 10, 95, 150, 60. What is the total head movement under SSTF scheduling?

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