Assume a disk has the following characteristics There are 1

Assume a disk has the following characteristics : There are 10 surfaces with 100,000 tracks each o Tracks hold an average of 1000 sectors of 1024 bytes each o 20% of each track is used for gaps o The disk rotates at 10,000 rpm o The time it takes the head to move n tracks is (1 + 0.0002n) milliseconds. Answer the following questions about the above disk drive: a) What is the capacity of the disk? b) What is the maximum seek time? c) What is the maximum rotational latency? d) If a block is 64 sectors (65,546 bytes), what is the transfer time of a block? e) What is the average seek time? f) What is the average rotational latency?

Solution

a) What is the capacity of the disk?
The disk has 10 * 10,0000 = 100,0000 tracks. . Thus, the capacity is 100,0000 *1000*1024

b) The maximumseek time occurs when the heads have to move across all the tracks. Thus,substitute 10,000 for n in the formula (1 + 0.0002n) = 1+ 2/10000*1000000 = 21ms


c) The maximum rotational latency is one full revolution. Since the disk rotates at 10,000 rpm, it takes 60/10000 of a minute, or 6 milliseconds.

d) 64 sectors with 63 gap and 1000 sector with 1000 gap
degrees = (64/1000 *10% + 63/1000 * 90% ) . * 360 = 23.004 degree
Time =. 23.004/360 * 10% = 63.9 ms

e) What is the average seek time. =   1 + 0.0002 * (100000/2) = 11 ms

f) Average rotational delay = max totational latency /2 = 5ms



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