Disk Average Seek Time HW Question?

Question

If somebody could help me with any of these 2 questions, I'd really appreciate it... The first and the last one.

Consider a single-platter disk with the following parameters: rotation speed: 7200 rpm; number of tracks on one side of platter: 30000; number of sectors per track: 600; seek time: one ms for every hundred tracks traversed. Let the disk receive a request to access a random sector on a random track and assume the head starts at track 0.

a. What is the average seek time?

b. What is the average rotational latency?
4.17 ms

c. What is the transfer time for a sector?
T=512/(7200)(307200)=2.31 ms or .00231 s

d. What is the total average time to satisfy a request?

Answer 1

These nubers are arbitrary. If you look at how each manufacturer measures these numbers isw a lesson in "new math".

Example: You fail to take into account the track to track seek and adjasent track seek time. both of these munbers are averaged into the "average random seek time". Also the dont use the whole swept time of the disk. (the time it takes the drive to spin one revolution) they use 1/2 to 3/4 of it, depending on the manu. If you have ever noticed 2 simmilar drives will perform different with the same specs. If you see some cheap Maxtor drives on sale dirt cheap in the store, you know why.

I will give no opinions on other manufacturers but check out the paperwork in a hard drive, it will surprise you.

Makes more sence when trying to figure this out if the average track to track is 2 ms how can you seek 500 tracks away in 9.2 ms.

Answer 2

Hi. "number of tracks on one side of platter: 30000; seek time: one ms for every hundred tracks traversed." The max seek time would be 30000/100 ms or 300 ms. The min seek time would be less that 1 ms. Assume 15000 is the track being accessed. 150 ms for head travel plus 4.17ms for rotational latency. I would guess about 154.7.