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Operating systems miscellaneous

  1. Consider a disk pack with a seek time of 4 milliseconds and rotational speed of 10000 Rotations Per Minute (RPM). It has 60 sectors per track and each sector can store 512 bytes of data. Consider a file stored in the disk. The file contains 2000 sectors. Assume that every sector access necessitates a seek, and the average rotational latency for accessing each sector is half of the time for one complete rotation. The total time (in milliseconds) needed to read the entire file is _______.
    1. 11020 ms
    2. 7020 ms
    3. 14020 ms
    4. 140 ms
Correct Option: C

Given that , Seek time = 4ms
60s → 10000 rotations
60s → 10000 rotations

60
= 6 ms ← 1 rotation time
10000

∴ Rotational Latency =
1
× 6 ms = 3 ms
2

1 track → 600 sectors
6ms ← 600 sectors (1 rotation means 600 sectors or 1 track)
1 sector →
6ms
= 0.01 ms
600

2000 sector → 2000 (0.01) = 20 ms
∴ Total time needed to read the entire tile is = 2000 (4 + 3) + 20
= 8000 + 6000 + 20 = 14020 ms



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