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Disk requests come to a disk driver for cylinders in the order 10, 22, 20, 2, 40, 6, and 38 at a time when the disk drive is reading from cylinder 20. The seek time is 6 ms/cylinder. The total seek time, if the disk arm scheduling algorithms is first-come-first-served is
  • a)
    360 ms
  • b)
    850 ms
  • c)
    900 ms
  • d)
    None of the above
Correct answer is option 'D'. Can you explain this answer?
Most Upvoted Answer
Disk requests come to a disk driver for cylinders in the order 10, 22,...
FCFS Total seek time in FCFS Scheduling when the disk drive is reading from cylinder 20 for cylinders in the order 10, 22, 20, 2, 40, 6, and 38 :
= (10 + 12 + 2 + 18 + 38 + 34 + 32)*6
= 146*6
= 876 ms
As no other option matches the answer, option (D) is correct.
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Community Answer
Disk requests come to a disk driver for cylinders in the order 10, 22,...
Total Seek Time Calculation
To calculate the total seek time for the disk requests using the First-Come-First-Served (FCFS) scheduling algorithm, we need to analyze the sequence of cylinder requests and their distances from the current position of the disk arm.
Initial Conditions
- Current cylinder: 20
- Sequence of requests: 10, 22, 20, 2, 40, 6, 38
- Seek time: 6 ms per cylinder
Request Sequence Analysis
The requests will be processed in the order they arrive. Starting from cylinder 20, let's calculate the movement for each request:
- From 20 to 10:
- Distance = |20 - 10| = 10 cylinders
- Seek time = 10 * 6 ms = 60 ms
- From 10 to 22:
- Distance = |10 - 22| = 12 cylinders
- Seek time = 12 * 6 ms = 72 ms
- From 22 to 20:
- Distance = |22 - 20| = 2 cylinders
- Seek time = 2 * 6 ms = 12 ms
- From 20 to 2:
- Distance = |20 - 2| = 18 cylinders
- Seek time = 18 * 6 ms = 108 ms
- From 2 to 40:
- Distance = |2 - 40| = 38 cylinders
- Seek time = 38 * 6 ms = 228 ms
- From 40 to 6:
- Distance = |40 - 6| = 34 cylinders
- Seek time = 34 * 6 ms = 204 ms
- From 6 to 38:
- Distance = |6 - 38| = 32 cylinders
- Seek time = 32 * 6 ms = 192 ms
Total Seek Time Calculation
Now, summing all these seek times:
- Total Seek Time = 60 ms + 72 ms + 12 ms + 108 ms + 228 ms + 204 ms + 192 ms = 876 ms
Thus, the total seek time is 876 ms, which does not match any of the options provided, confirming that the correct answer is option 'D' (None of the above).
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Disk requests come to a disk driver for cylinders in the order 10, 22, 20, 2, 40, 6, and 38 at a time when the disk drive is reading from cylinder 20. The seek time is 6 ms/cylinder. The total seek time, if the disk arm scheduling algorithms is first-come-first-served isa)360 msb)850 msc)900msd)None of the aboveCorrect answer is option 'D'. Can you explain this answer?
Question Description
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