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Consider a disk system having $60$ cylinders. Disk requests are received by a disk drive for cylinders $10,22,20,2,40,6$ and $38$, in that order. Assuming the disk head is currently at cylinder $20$, what is the time taken to satisfy all the requests if it takes $2$ milliseconds to move from one cylinder to adjacent one and Shortest Seek Time First (SSTF) algorithm is used?

  1. $240$ milliseconds
  2. $96$ milliseconds
  3. $120$ milliseconds
  4. $112$ milliseconds
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Disk requests with head at 20

2  6 10  20  22  38  40

20--->22---->10--->6---->2------>38------>40 total head movements (2+12+4+4+36+2) =60

 

time= 60x2= 120ms option 3 is the ans

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