# Homework 6

1. Problem 8.5 on page 342 in the textbook.

2. [Exam '96] A company makes a unit that is to replace diskettes. Each unit contains two platters and can store 1GB. The platters spin at 5400 RPM and it is reveled that the transfer rate for a short time is 10MB/sec.

a) What does this tell us about the amount of data on each cylinder and how many are the cylinders? (The number of cylinders is the same as the number of tracks on each side of a platter).

b) Now it is also reveled that the maximum sustained transfer time is 6.6MB/sek. What does that tell us about the seek time between adjacent tracks and what is the average access time of the unit?

[Makeup exam '99] A disk drive has 4 platters and 8 heads. Each side has 13295 tracks. The total storege space of the disk is 17,28 GB (where GB is in this case 1.000.000.000 bytes). The number of sectors is variable, from 230 to 384. Each sector contains 512 bytes.

1. What is the average number of sectors per track, based on the total storage space of the disk?
2. If the disk spins at 5400 RPM, what is the maximum transfer rate (assuming that only one head reads at a time)?
3. If it takes 0.9 msec to move the heads between adjacent tracks what is the sustained transfer rate)?

3. Most disk drives use a stagger when writing on more than one track. That means tha when done with writing on one track, finishing on sector i, then we do not write in sector i+1 on the next track, but rather sector i+7, for instance
1. What is the reason for this?
2. If a disk with 240 sectors spins at 7200 RPM and takes 1.5 msec to move the head between adjacent tracks, what would then be the best stagger (counted in sectors)?

4. Compare the transfer rates of a 40x CD-ROM and a 8x DVD-ROM. To answer this question you will have to make some assumptions and look for information on the Net. Write out the assumptions that you are making.

Hand these problems in on monday december 3rd.

hh (hja) hi.is, november 27th, 2001.