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 total head movement of cylinders for the C-SCAN disc Scheduling technique if the head starts moving in the right direction from initial position?
Answer: D. 385 — Key assumption: cylinders are numbered from 0 to 199. Service order for C-SCAN when starting at 58 and moving right: First service requests to the right of 58…
- A.
327
- B.
307
- C.
525
- D.
385
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Show answer & explanation
Correct answer: D
Key assumption: cylinders are numbered from 0 to 199.
Service order for C-SCAN when starting at 58 and moving right:
First service requests to the right of 58 in ascending order: 77, 81, 99, 150, 175, 185.
Then move to the end of the disk (199), wrap around to 0, and service remaining requests in ascending order: 33, 45.
Compute each movement (in cylinders):
58 → 77 = 19
77 → 81 = 4
81 → 99 = 18
99 → 150 = 51
150 → 175 = 25
175 → 185 = 10
185 → 199 = 14 (move to disk end before wrap)
199 → 0 = 199 (wrap-around counted as full disk traversal for C-SCAN)
0 → 33 = 33
33 → 45 = 12
Sum of movements: 19 + 4 + 18 + 51 + 25 + 10 + 14 + 199 + 33 + 12 = 385 cylinders.
Therefore, the total head movement for C-SCAN (starting at 58, moving right, disk 0–199) is 385 cylinders.
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