Consider a disk with tracks numbered 0 to 199. The current head position is 50 (Head Movement is Left). The request queue is: 98, 183, 37, 122, 14, 124, 65, 67. How Many Head movements are there in servicing requests using C-LOOK?Tip: Enter numerical data ONLY. E.g: "5" and NOT "5 Head Movements".

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BlackTom AI · Accepted Answer

Question restatement: A disk has tracks 0–199. Head initially at 50 with movement direction Left. Request queue: 98, 183, 37, 122, 14, 124, 65, 67. We must compute total head movements using C-LOOK.

First, identify which requests lie to the left of the starting head (i.e., <= 50) and which lie to the right (i.e., > 50).
- Left of 50: 37 and 14.
- Right of 50: 98, 183, 122, 124, 65, 67.

Under C-LOOK with a leftward start, the head services all left-side requests while moving left, in decreasing order from the starting point. From 50, the next leftward requests are 37, then 14. The movements are:
- 50 -> 37: distance 13
- 37 -> 14: distance 23
Total for the leftward sweep: 13 + 23 = 36 movements.

Next, C-LOOK uses a wrap-around (jump) to the furthest-right request, but this wrap is not counted in the total head movement. That is, the jump from the leftmost serviced track (14) to the rightmost unserved track (183) is instantaneous for the purposes of counting movements.

Now service the remaining right-side requests in decreasing order (since we continue in the same leftward direction after the wrap): 183, 124, 122, 98, 67, 65.
- 183 -> 124: distance 59
- 124 -> 122: distance 2
- 122 -> 98: distance 24
- 98 -> 67: distance 31
- 67 -> 65: distance 2
Total for the rightward sweep after wrap: 59 + 2 + 24 + 31 + 2 = 118 movements.

Combine the two sweeps, excluding the wrap jump from the total (as per C-LOOK convention): 36 (left sweep) + 118 (right sweep) = 154 movements.

All steps rely on the principle that, in C-LOOK, the wrap from one end to the other is not counted in the total head movement, which is the key source of the 154 total in this scenario.

Consider a disk with tracks numbered 0 to 199. The current head position is 50 (Head Movement is Left). The request queue is: 98, 183, 37, 122, 14, 124, 65, 67. How Many Head movements are there in servicing requests using C-LOOK?Tip: Enter numerical data ONLY. E.g: "5" and NOT "5 Head Movements".

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