Consider a disk with the following characteristics: block size B = 512 bytes, in

Question

Consider a disk with the following characteristics: block size B = 512 bytes, interblock gap is G = 128 bytes, the number of blocks per track is 20, and the number of tracks per surface is 400. A disk pack consists of 15 double-sided disks and rotates the disks at a speed of 2400 rpm and it has an average seek time of 30 msec. Then,

a. Transfer rate tr in bytes/msec is: tr = bytes per msec.

b. Block transfer time btt in msec is: btt = msec.

c. Average rotational delay rd in msec is: rd = msec.

d. It takes msec to locate and transfer a single block given its block address.

Explanation / Answer

Given:

disk characteristics

block size B=512 bytes

interblock gap is G=128 bytes

number of blocks per track is 20

number of tracks per surface is 400

disk pack consists of 15 double sided disks

the disk rotates at a speed of 2400 rpm

and average seek time of 30 msec

a) transfer rate tr in bytes/msec is: tr = bytes per msec

Transfer rate tr= (total track size in bytes)/(time for one disk revolution in msec)

time for one disk revolution in msec = ((60*1000)/disk rotation speed)

= ((60*1000)/2400)

= 25

tr = 12800/25

= 512 bytes/msec

therefore transfer rate is 512 bytes/msec

b) Block transfer time btt in msec is: btt = msec.

block transfer time btt = Block size(B) / transfer rate(tr)

btt = 512 / 512

= 1 msec

therefore block transfer time is 1 msec

c) Average rotational delay rd in msec is: rd = msec.

average rotational delay rd = (time for one disk revolution in msec) / 2

time for one disk revolution in msec = ((60*1000)/disk rotation speed)

= ((60*1000)/2400)

= 25

rd = 25 / 2

= 12.5 msec

therefore average rotational delay is 12.5 msec

d)It takes msec to locate and transfer a single block given its block address.

average time to locate and transfer a block = seek time(s)+rotational delay(rd)+block transfer time(btt)

= 30+12.5+1

= 43.5 msec

therefore average time to locate and transfer a single block in given block address is 43.5 msec

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