In one rotation, how many sectors are passed over and how many tracks are passed over?

If you know the average value of sectors per track for a hard drive, how do you use this to estimate the number of cylinders?

Do all modern hard drives have 63 sectors per track? Are there any hard drives that have more than this?


3 Answers 3


Almost all modern hard drives report 63 sectors per track, because that's the maximum allowed by the BIOS specs.

This number (along with heads and cylinders) is of course fake and used only for compatibility addressing with very old programs. Internally they use a simple sector number starting from 0 (called LBA mode).

The real sector per track number is not only much larger, but it also varies depending on the distance from the spindle. See, for example, this page from the makers of HDDScan.

  • This is correct.
    – Alex
    Mar 13, 2010 at 9:18
  • Ah the days of CHS; how I do not miss them. Even with a formula, it was still difficult to get the numbers to work.
    – Synetech
    Sep 13, 2011 at 6:28

No easy way to say - every hard drive is different and has different density, on top of this, there are obviously more the further away from the centre you are as the circles become wider.

Pick a model, and give a bit more information (such as the outer most circle) and I will try to help you further.

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As the disk spins, sectors travel under the read head at a rate that depends on the RPM of the disk. So the transfer rate is the rotation rate times the number of sectors in a track times the number of bytes in a sector.

(RPM / 60) * Sectors-per-track * bytes-per-sector = bytes-per-second
  • Where do I plug in the media transfer rate into this equation?
    – Phenom
    Feb 11, 2010 at 20:27
  • bytes-per-second is the transfer rate.
    – John Knoeller
    Feb 11, 2010 at 20:55

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