Consider the following disc Queue with requests for I/O to block on cylinders:…
2025
Consider the following disc Queue with requests for I/O to block on cylinders:
45, 81, 185, 33, 175, 99, 150, 77
(Consider that the head starts from location 58)
What shall be the 2nd request being processed by SCAN (LEFT) disc Scheduling technique for the already given request queue?
Answer: C. 33 — Key insight: SCAN (LEFT) moves the head toward lower cylinder numbers first and services requests as it encounters them. Steps to determine the order: Start…
- A.
81
- B.
45
- C.
33
- D.
175
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Correct answer: C
Key insight: SCAN (LEFT) moves the head toward lower cylinder numbers first and services requests as it encounters them.
Steps to determine the order:
Start position: 58. Separate requests into those left of 58 and those right of 58.
Requests left of 58: 45, 33. Requests right of 58: 77, 81, 99, 150, 175, 185.
Because the head moves left, it will service left-side requests in order of decreasing cylinder number encountered while moving toward 0: first 45 (closest), then 33.
Result: the first request serviced is 45 and the second request serviced is 33.
Final answer: 33
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