Consider a disk sequence with 100 cylinders. The request to access the…
2017
Consider a disk sequence with 100 cylinders. The request to access the cylinder occur in the following sequence : 4, 34, 10, 7, 19, 73, 2, 15, 6, 20 Assuming that the head is currently at cylinder 50, what is the time taken to satisfy all requests if it takes 2 ms to move from one cylinder to adjacent one and shortest seek time first policy is used?
Answer: B. 238 — Under the Shortest Seek Time First (SSTF) policy, the disk arm services the request closest to its current position. From 50:Nearest = 34 → movement = |50 −…
- A.
190
- B.
238
- C.
233
- D.
276
Attempted by 168 students.
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Correct answer: B
Under the Shortest Seek Time First (SSTF) policy, the disk arm services the request closest to its current position.
From 50:
Nearest = 34 → movement = |50 − 34| = 16
From 34:
Nearest = 20 → |34 − 20| = 14
From 20:
Nearest = 19 → |20 − 19| = 1
From 19:
Nearest = 15 → |19 − 15| = 4
From 15:
Nearest = 10 → |15 − 10| = 5
From 10:
Nearest = 7 → |10 − 7| = 3
From 7:
Nearest = 6 → |7 − 6| = 1
From 6:
Nearest = 4 → |6 − 4| = 2
From 4:
Nearest = 2 → |4 − 2| = 2
From 2:
Remaining = 73 → |2 − 73| = 71
Total distance traveled = 16+14+1+4+5+3+1+2+2+71=119
Time taken = 119cylinders * 2 ms/cylinder = 238 ms.
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