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

Question

BlackTom AI · Accepted Answer

We start with the disk head at track 50 and the request queue: 98, 183, 37, 122, 14, 124, 65, 67. Using the SSTF (Shortest Seek Time First) strategy, at each step we pick the pending request closest to the current head position.

Step 1: From 50, distances to each request: |98-50|=48, |183-50|=133, |37-50|=13, |122-50|=72, |14-50|=36, |124-50|=74, |65-50|=15, |67-50|=17. The smallest distance is 13 to 37. Move to 37. Cumulative movements: 13.

Step 2: Now at 37, remaining requests: 98, 183, 122, 14, 124, 65, 67. Distances: |98-37|=61, |183-37|=146, |122-37|=85, |14-37|=23, |124-37|=87, |65-37|=28, |67-37|=30. The smallest distance is 23 to 14. Move to 14. Cumulative movements: 13+23=36.

Step 3: At 14, remaining: 98, 183, 122, 124, 65, 67. Distances: |98-14|=84, |183-14|=169, |122-14|=108, |124-14|=110, |65-14|=51, |67-14|=53. The smallest is 51 to 65. Move to 65. Cumulative: 36+51=87.

Step 4: At 65, remaining: 98, 183, 122, 124, 67. Distances: |98-65|=33, |183-65|=118, |122-65|=57, |124-65|=59, |67-65|=2. The smallest is 2 to 67. Move to 67. Cumulative: 87+2=89.

Step 5: At 67, remaining: 98, 183, 122, 124. Distances: |98-67|=31, |183-67|=116, |122-67|=55, |124-67|=57. The smallest is 31 to 98. Move to 98. Cumulative: 89+31=120.

Step 6: At 98, remaining: 183, 122, 124. Distances: |183-98|=85, |122-98|=24, |124-98|=26. The smallest is 24 to 122. Move to 122. Cumulative: 120+24=144.

Step 7: At 122, remaining: 183, 124. Distances: |183-122|=61, |124-122|=2. The smallest is 2 to 124. Move to 124. Cumulative: 144+2=146.

Step 8: At 124, remaining: 183. Distance to 183 is |183-124|=59. Move to 183. Final cumulative movements: 146+59=205.

Therefore, the total head movements required to service all requests using SSTF is 205.

System Software and Computing Concepts (032025-ABB)

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

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