Average and minimum times for reading and writing to storage devices are common

Question

Average and minimum times for reading and writing to storage devices are common measurements used to compare devices. Using techniques from Chapter 6, calculate values related to read and write time for disks with the following characteristics. Calculate the average time to read or write a 1024-byte sector for each disk listed in the table. Calculate the minimum time to read or write a 2048-byte sector for each disk listed in the table. For each disk in the table, determine the dominant factor for performance. Specifically, if you could make an improvement to any aspect of the disk, what would you choose? If there is no dominant factor, explain why.

Explanation / Answer

Solution:

6.3.1 For machine a

To read the data

average time will be= seek time+average rotational latency+transfer time+Controller overhead time

Average rotational latency= 1/2*(60/7500)= 4 ms

Transfer time= 1024/(90*2^20)= 0.01085069 ms

Controller overhead time= 1024/(100*2^20)= 0.00976562 ms

Average time= 10+4+0.01085069 +0.00976562= 14.02061631 ms

For machine b

to read

average time= 7* 10^(-3)+1/2*(60/10000)+ 1024/(40*2^20)+ 1024/(200*2^20)= 10.02929687 ms

6.3.2

Minimum time will be achieved when our head for reading the data directly lands at the right sector this way we can remove the latency time

So minimum time for a

Minimum time= 10+0.01085069 +0.00976562= 10.02061631

and for machine b

Minimum time= 7* 10^(-3)+ 1024/(40*2^20)+ 1024/(200*2^20)= 7.02929687 ms
6.3.3

The dominant factor is seek time and rotatoinal time for performance if we can decrease taht somehow we can improve our performance very efficiently.

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