Calculating the Transfer Time for a Hard Disk

Question

I know that transfer rate is data size over transfer speed - but according to the information given, I don't know what the data size is to calculate the transfer rate. Am I missing something or was I really not given it?

The information given is as follows:

A number of files are stored on a 10000RPM hard disk. The platters rotate clockwise. The heads move at the speed of 250 centimeters per second. The controller overhead of the hard disk is 0.2 milliseconds per I/O request. The data transfer speed is 100 MB/s. Assume one I/O request is sent for every file. The average seeking distance is 1 centimeter. Since a sector is very small, ignore the time to rotate it through under the head. Calculate the average time to fetch data for each of the scenarios below.

a. 1 file of 10 sectors is fetched. The sectors are randomly distributed on the disk.

I know I need the transfer rate to calculate fetch time - but again - I don't know the data size so I don't know how to calculate it.

Answer 1

Sectors are usually 512B to 4KB. In your case, it seems that the actual time it takes to read the sectors is negligible compared to seeking (verify this!), and this could be what is meant by the following line:

Since a sector is very small, ignore the time to rotate it through under the head.

To be sure, make the calculation with respect to the largest sector size (4KB), and check that the data transfer time is negligible. If it isn't, you are indeed missing a data point.