0
\$\begingroup\$

Given a disk drive that has disk sector and track (as given in diagram in Wikipedia), are the 2 structures physically implemented on the drive or are they logical implementations?

I am not asking about any specific disk drive model or any particular version. Any latest disk drive having sector and track would do. It's just I was curious what kind of implementations were those.

\$\endgroup\$
4
  • 2
    \$\begingroup\$ At the actual computer-disk interface, cylinder-head-sector addressing has not been commonly used for a long time - disks are addressed with LBA. As for the on-disk format, this may very well be proprietary and kept well-guarded by disk vendors - I am myself limited by NDA from discussing this. \$\endgroup\$
    – nanofarad
    Apr 4, 2022 at 19:21
  • 1
    \$\begingroup\$ There was a very informative YouTube video about this recently. I’ll try to dig it up. During manufacturing back in the day, sectors were hard coded into the magnetic material on the disk in order to facilitate something concerning timing and data structure on the logical level. I doubt any part of the disk is wasted for that these days. \$\endgroup\$
    – winny
    Apr 4, 2022 at 20:08
  • 1
    \$\begingroup\$ All HDD's now are hard sectored with servo dibits between tracks and embedded servo tracking. Soft Sectors are thus created knowing these sector boundaries with your format. Full physical tracks can be buffered if necessary starting from any LBA. Transfer Rates to random sectors double in speed with block size doubling. until limited by channel. Although I must admit not keeping up to all the secrets of compression , variable physical block sizes, Zone recording speed changes with density , spares and ECC algorithms with relocation, SATA down-shifting etc \$\endgroup\$ Apr 4, 2022 at 20:10
  • \$\begingroup\$ They are physical, but they are now internal details of the drive. The operating system doesn't get to know about them. Old operating systems did. \$\endgroup\$ Apr 4, 2022 at 20:31

2 Answers 2

2
\$\begingroup\$

It may not apply to modern drives any more, but that is exactly how hard drives and floppy drives worked and accessed data.

You can move a read/write head on a surface to a certain track/cylinder (or stack of multiple heads on multiple platters in case of hard drives) with a stepper motor or voice coil.

The circular track is divided into sectors which can be individually read or written when they appear under the head as the surface rotates.

However, as the inner tracks have slower linear velocity than the outer tracks, even in early computing days tracks could have different amount of sectors depending on the location of the track. And to abstract it away, the drive may just present the user with constant amount of cylinders, heads, and sectors, i.e. a virtual or logical geometry that is separate from physical geometry.

In many systems though, even if drives internally have some physical amount of heads, tracks and sectors, and have converted that to some logical geometry other than the physical geometry, they have been mainly accessed in linear fashion for a long time now, so cylinder, heads and sectors are not so important.

\$\endgroup\$
1
\$\begingroup\$

The properties of the magnetic surface and the disk heads determine the minimal track width, track distance and the tangential length of a bit. So the number of tracks is given by physical limits. The number of sectors is a result of these limits too.

The circumference of an inner track is much smaller than that of an outer track. So there are less sectors on an inner track than on the outmost track.

The disk controller should set the internal number of tracks, sectors and heads.

The external organisation of the disk may be much different. The number of logical sectors per track is constant, there may be more logical heads than physical heads. The number of logical tracks may be different to the physical number.

A later improved version of the same disk model may use another internal physical organisation with different numbers of tracks and sectors.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.