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Homework Help: Magnetic disk

  1. Sep 13, 2011 #1
    1. The problem statement, all variables and given/known data

    Suppose the hard disk above has 1024 cylinders, 8 tracks per cylinder, 32 sectors per track and 512 Bytes per sector. The maximum seek time is 450 msec, the time to move between adjacent cylinders is 10 msec, the rotation time is 14.

    a) If the entire disk was full of data stored consecutively, how much time would it take to read the entire disk if the read/write head is already positioned on the first sector of the first track of the first cylinder of the disk?

    b) Find the total capacity of the disk?

    c) Find the maximum access time (worst case) for 800KB of data not stored on consecutive tracks. Clearly explain your solution/working.

    2. Relevant equations and 3. The attempt at a solution

    1024 cylinders
    8 tracks/ cylinder (8192 tracks)
    32 sectors/ track (262144 sectors)
    512 bytes/ sector (134217728 bytes)
    Maximum seek = 450 ms
    Switch/wait = 10ms + 4ms
    Latency(rotational time) = 14 ms

    a) Total time = number of tracks × rotational time
    = 8192 tracks×14 ms
    = 114688 ms

    b) Total capacity = cylinders×tracks×sectors×512 bytes
    = 1024 cylinders×8 tracks×32 sectors×512 bytes
    = 134217728 bytes
    = 134217728 bytes÷2^20
    = 128 MBytes

    c) Maximum access time = seek + latency + transfer + switch/wait

    #tracks = (800×2^10 )bytes×(1 sector)/(512 bytes)×(1 track)/(32 sectors)
    = 50 tracks

    Transfer time = #tracks ×rotational time
    = 50 tracks × 14 ms
    = 700ms

    Switch/ wait = 10ms +4ms = 14ms

    Maximum access time = seek + latency + transfer + switch/wait
    = 450ms+14ms+700ms+98ms
    = 1262ms
  2. jcsd
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