# Calculating the maximum number of sectors per track for a hard disk

If you know the media transfer rate of a hard disk, how do you use that information to calculate the maximum number of sectors per track?

-
You can't. Too many other variables make it an impossibility. – John Gardeniers Feb 12 '10 at 0:24

If a sector is a known size (in bytes), you know the rpm of the drive, you know the maximum transfer rate* (in Megabytes/sec or somesuch) it should be fairly straightforward to work out the maximum number of sectors on a track.

I say "should be" because you're not being given enough data for a modern drive. You'll have to assume that the number of sectors per track is constant over the area where you are measuring the maximum transfer rate for starters. It probably is but it might not be, so the best you can get using these numbers is a pretty close estimate provided the drive is physically simple. Unfortunately drives are not physically simple anymore.

To expand on Michael Graff's answer - there is a lot going on at the physical level (remapping of sectors, variable track geometry, multiple heads and more) that will make it hard to give an absolute answer. Sector interleaving would completely throw any calculations out too but that is rare in modern drives as far as I'm aware. For drives with multiple physical platters and multiple heads you have to adjust for that too - for example on a drive with six read\write heads on three platters, there might be 200 sectors per track, (on each side of a platter) but there will be 1200 sectors per cylinder.

If you know the physical structure of the drive (number of read/write heads), you know that it's pretty healthy (so there are no significant amount of remapped sectors), you know that it doesn't use interleaving and you know that the read test you carried out was thorough enough to swamp any cache effects, then you can make a reasonable calculation based on the rpm of the drive and the maximum transfer rate.

-
What would the equation be? – Phenom Feb 11 '10 at 21:24
Seriously the answer is in the first paragraph. I was hoping to help you understand the reason someone gave you this as homework (you get to understand somethings about how drives work) but you still need to make some effort to work it out. – Helvick Feb 11 '10 at 22:09

You probably cannot. Even wimpy hard drives have caches and one logical track is not the same as a physical track anymore.

-
I think that theoretically it's possible since this is a homework assignment for a programming class. – Phenom Feb 11 '10 at 20:21
@Phenom if your asking homework questions, then you should really let us know that in the question, and show us what you have tried so far. Were more than happy to help you if you get stuck with homework questions, but you need to show you have put some effort in first, we are not just going to do your homework for you. – Sam Feb 12 '10 at 9:50