GATE | GATE-CS-2016 (Set 1) | Question 58

Consider a disk queue with requests for I/O to blocks on cylinders 47, 38, 121, 191, 87, 11, 92, 10. The C-LOOK scheduling algorithm is used. The head is initially at cylinder number 63, moving towards larger cylinder numbers on its servicing pass. The cylinders are numbered from 0 to 199. The total head movement (in number of cylinders) incurred while servicing these requests is:
Note : This question was asked as Numerical Answer Type.

(A) 346
(B) 165
(C) 154
(D) 173

Answer: (B)

Explanation: The head movement would be :

63 => 87 24 movements
87 => 92 5 movements
92 => 121 29 movements
121 => 191 70 movements
191 --> 10 0 movement
10 => 11 1 movement
11 => 38 27 movements
38 => 47 9 movements

Total head movements = 165

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