A memory has 8 megabytes of cells (a) What is the size of its MAR? (b) If 2-dime

Question

A memory has 8 megabytes of cells

(a) What is the size of its MAR?

(b) If 2-dimensional addressing is used, what is the size of each of the horizontal and vertical decoders?

Assume that a hard disk has the following characteristics: Rotation speed = 7,200 rev/min Arm movement time = 0.5msec fixed start-up time + 0.05 msec for each track crossed Number of surfaces = 2 (double-sided disk) Number of tracks per surface = 500 Number of sectors per track = 20 Number of characters per sector = 1,024

(a) How many characters can be stored on the disk?

(b) What are the best case and worst case access time for the data (in a sector)?

Explanation / Answer

a)Number of characters stored in a disk. = 1,024 * 20 * 500 * 2 = 20480000 characters .

b) The best case occur when the correct sector is under the read/write head = 0.05 msec

Worst case occur when it is on the farthest track and the farthest sector :-

0.05msec + 0.05msec*499+ 60 seconds*1/7,200   = 200 + 0.05 + 24.95    = 225 ms

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