OS Day 2 Part 2

Which of the following statements is not true about disk-arm scheduling algorithms ?

• SSTF (shortest seek time first) algorithm increases performance of FCFS

• The number of requests for disk service are not influenced by file allocation method.

• Caching the directories and index blocks in main memory can also help in reducing disk arm movements.

• SCAN and C-SCAN algorithms are less likely to have a starvation problem.

Assuming that the disk head is located initially at 32, find the number of disk moves required with FCFS if the disk queue of I/O block requests are 98, 37, 14, 124, 65, 67 :

• 310

• 321

• 320

• 324

On a disk with 1000 cylinders (0 to 999) find the number of tracks, the disk arm must move to satisfy all the requests in the disk queue. Assume the last request service was at track 345 and the head is moving toward track 0. The queue in FIFO order contains requests for the following tracks :123, 874, 692, 475, 105, 376(Assume SCAN algorithm)

• 2013

• 1219

• 1967

• 1507

Consider a disk queue with request for input/output to block on cylinders 98, 183, 37, 122, 14, 124, 65, 67in that order. Assume that disk head is initially positioned at cylinder 53 and moving towards cylinder number 0. The total number of head movements using Shortest Seek Time First (SSTF) and SCAN algorithms are respectively

• 236 and 252 cylinders

• 640 and 236 cylinders

• 235 and 640 cylinders

• None of the above

If the disk head is located initially at 32, find the number of disk moves required with FCFS if the disk queue of I/O blocks requests are 98, 37, 14, 124, 65, 67.

• 239

• 310

• 321

• 325

Consider the input/output request node at different time directed at a hyphothetical disk have 200 tracks as given in the following table:

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Assume that : Current Head position is at track no.65

Current Clock Time 160 millisec

• 144 and 123 milliseconds

• 143 and 123 milliseconds

• 149 and 124 milliseconds

• 256 and 186 milliseconds