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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?
  • a)
    190
  • b)
    38
  • c)
    233
  • d)
    276
Correct answer is option 'B'. Can you explain this answer?
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Most Upvoted Answer
Consider a disk sequence with 100 cylinders. The request to access the...
To find the time taken to satisfy all requests using the shortest seek time first policy, we need to calculate the total seek time for each request and sum them up.

Given:
Disk sequence: 4, 34, 10, 7, 19, 73, 2, 15, 6, 20
Current head position: 50
Time to move from one cylinder to adjacent one: 2 ms

Step 1: Calculate the seek time for each request
To calculate the seek time for each request, we need to find the absolute difference between the current head position and the requested cylinder.

- Seek time for 4: |50 - 4| = 46
- Seek time for 34: |50 - 34| = 16
- Seek time for 10: |50 - 10| = 40
- Seek time for 7: |50 - 7| = 43
- Seek time for 19: |50 - 19| = 31
- Seek time for 73: |50 - 73| = 23
- Seek time for 2: |50 - 2| = 48
- Seek time for 15: |50 - 15| = 35
- Seek time for 6: |50 - 6| = 44
- Seek time for 20: |50 - 20| = 30

Step 2: Sort the requests based on seek time
Arrange the requests in ascending order of seek time. This is the shortest seek time first policy.

- Sorted requests: 73, 2, 6, 7, 10, 20, 15, 19, 34, 4

Step 3: Calculate the total seek time
To calculate the total seek time, we sum up the seek time for each request.

Total seek time = 73 + 2 + 6 + 7 + 10 + 20 + 15 + 19 + 34 + 4 = 190

Step 4: Calculate the total time taken
Since it takes 2 ms to move from one cylinder to an adjacent one, we need to multiply the total seek time by 2 to get the total time taken.

Total time taken = 190 * 2 = 380 ms

Therefore, the time taken to satisfy all requests using the shortest seek time first policy is 380 ms, which corresponds to option B.
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Consider a disk sequence with 100 cylinders. The request to access the...
4, 34, 10, 7, 19, 73, 2, 15, 6, 20 Since shortest seek time first policy is used, head will first move to 34. This move will cause 16*2 ms. After 34, head will move to 20 which will cause 14*1 ms. And so on. So cylinders are accessed in following order 34, 20, 19, 15, 10, 7, 6, 4, 2, 73 and total time will be (16 + 14 + 1 + 4 + 15 + 3 + 1 + 1 + 1 + 71)*2 = 238 ms. So option (B) is correct.
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Consider a storage disk with 4 platters (numbered as 0, 1, 2 and 3), 200 cylinders (numbered as 0, 1, … , 199), and 256 sectors per track (numbered as 0, 1, … , 255). The following 6 disk requests of the form [sector number, cylinder number, platter number] are received by the disk controller at the same time: [120, 72, 2] , [180, 134, 1] , [60, 20, 0] , [212, 86, 3] , [56, 116, 2] , [118, 16, 1] Currently the head is positioned at sector number 100 of cylinder 80, and is moving towards higher cylinder numbers. The average power dissipation in moving the head over 100 cylinders is 20 milliwatts and for reversing the direction of the head movement once is 15 milliwatts. Power dissipation associated with rotational latency and switching of head between different platters is negligible. The total power consumption in milliwatts to satisfy all of the above disk requests using the Shortest Seek Time First disk scheduling algorithm is _______. Correct answer is '85'. Can you explain this answer?

Consider a storage disk with 4 platters (numbered as 0, 1, 2 and 3), 200 cylinders (numbered as 0, 1, … , 199), and 256 sectors per track (numbered as 0, 1, … 255). The following 6 disk requests of the form [sector number, cylinder number, platter number] are received by the disk controller at the same time: [120, 72, 2], [180, 134, 1], [60, 20, 0], [212, 86, 3], [56, 116, 2], [118, 16, 1] Currently head is positioned at sector number 100 of cylinder 80, and is moving towards higher cylinder numbers. The average power dissipation in moving the head over 100 cylinders is 20 milliwatts and for reversing the direction of the head movement once is 15 milliwatts. Power dissipation associated with rotational latency and switching of head between different platters is negligible. The total power consumption in milliwatts to satisfy all of the above disk requests using the Shortest Seek Time First disk scheduling algorithm is ______ .Note -This was Numerical Type question.

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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?a)190b)38c)233d)276Correct answer is option 'B'. Can you explain this answer?
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