Assume that a hard disk has the following characteristics: Rotation speed=7,200

Question

Assume that a hard disk has the following characteristics:
Rotation speed=7,200 rev/min arm; Arm movement time=0.5 msec fixed startup time+0.05 msec for each track crossed. (the startup time is a constant no matter how far the arm moves.) Assume on average the disk arm must move 150 tracks. Number of surfaces=2 (This is a double-sided disk. A single read/write arm holds both read/write heads.) Number of tracks per surface=500 number of sectors per track=20; Number of characters per sector=1,024. Now a.) How many characters can be stored on a single floppy disk? b.) What are the best-case,worst-case,and average-case access times for this disk? c.) What are the best case, worst case and average case access times for this disk if we increase the rotational speed to 9,600 rpm?
d.) What is the worst case time required to read the entire contents of the disk? Assume the read arm is initially positioned at the beginning of the first sector of the first track, and that every track must be read from the very beginning, that is, from the very first sector on that track.

Explanation / Answer

answer: a) characters can be stored on a single floppy disk = 1,024 characters * 20 sectors * 500 tracks * 2 surfaces = 20480000 characters per disk b)best case time its on the right track and the correct sector is under the read/write head = 0.05msec (startup) worst case it is on the farthest track and the farthest sector: 0.05msec (startup) + 0.05msec*499(max # of tracks to be traversed) + 60 seconds*1/7,200(time it takes for a whole revolution.

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