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 if the FCFS disc scheduling method is used?
Answer: C. 647 — Answer: 647 cylinders total head movement. Key idea: For FCFS (First-Come, First-Served), service happens in the given request order. Compute the absolute…
- A.
536
- B.
594
- C.
647
- D.
700
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Correct answer: C
Answer: 647 cylinders total head movement.
Key idea: For FCFS (First-Come, First-Served), service happens in the given request order. Compute the absolute distance between consecutive positions starting from the initial head position and sum them.
58 → 45 : |58 - 45| = 13 (cumulative 13)
45 → 81 : |45 - 81| = 36 (cumulative 49)
81 → 185 : |81 - 185| = 104 (cumulative 153)
185 → 33 : |185 - 33| = 152 (cumulative 305)
33 → 175 : |33 - 175| = 142 (cumulative 447)
175 → 99 : |175 - 99| = 76 (cumulative 523)
99 → 150 : |99 - 150| = 51 (cumulative 574)
150 → 77 : |150 - 77| = 73 (cumulative 647)
Total head movement = 13 + 36 + 104 + 152 + 142 + 76 + 51 + 73 = 647
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