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. The head is moving towards higher cylinders. What is the total head movement under LOOK scheduling?
Correct answer B. 280 cylinders
Explanation
LOOK travels only as far as the last request in each direction. Going up it serves 95, 120, 150 and 180 (110 cylinders), then reverses and serves 60, 35 and 10 (170 cylinders), a total of 280. SCAN would continue to cylinder 199 before turning, adding 38 cylinders to give 318. Avoiding that pointless travel to the edge is LOOK's advantage.
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