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(fdutils.info)More cylinders

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More Cylinders
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   Many nominally 40-cylinders or 80-cylinder drives are capable of more
cylinders, usually 41 and 83 respectively.  These can be used to get
extra capacity.  However, not all drives can seek to these unofficial
extra cylinders, and even on drives which can, these extra cylinders
tend to be less reliable.

   *WARNING*: Although most drives are able to use 83 cylinders, some
may not.  If your drive is making strange noises while accessing these
tracks.

   Although most drives support more than 80 tracks, I have heard rumors
that some do not, and repeatedly trying to read beyond track 80 might be
damaging to them.  In order to know wether your drive supports more than
eighty tracks, first set the number of allowed tracks to 82.  (using
`floppycontrol --cylinders 82 -d 'DRIVE)

   Then format a disk with a 82 track format (for example
`/dev/fd0H1722'), and copy on or several files to the disk until there
are less than 18 KB of free space on the disk.  Then eject and reinsert
the disk, and compare the files on the disk with the originals. If they
are the same, your drive does support 82 tracks. If so, you might want
to go further and try with 83 cylinders: `/dev/fd0H1743') This single
experience should not damage the drive, although repeating it many
times may be dangerous.

   If you do have a drive which supports more than 80 cylinders, you
have to call `floppycontrol --cylinders 82 DRIVE' before you can use
the extra cylinders.  You may put this line into your `/etc/rc.local',
so that the driver is automatically configured for the addition
cylinder after each boot.

   If on the other hand your drive doesn't support more than 80 tracks,
you should remove the entries for formats 13-19 from your `/dev'
directory after running `MAKEFLOPPIES', and you should call
`floppycontrol --cylinder 80 DRIVE' from your `/etc/rc.local' (or
`floppycontrol --cylinder 40 DRIVE' for 5 1/4 DD drives).

   By default, 83 cylinder are enabled for any high density and double
density drives.  3 1/2 double density drives have 80 cylinders enables,
and 5 1/4 double density drives have 40 enabled.

   *Usage:* These disks can be booted from using LILO, and can be
accessed in MS-DOS using `vgacopy'.

   *Interesting Formats:*

   All formats presented in the two previous sections may be amended to
use 83 cylinders instead of 80. Just add the `cyl=83' to the format
description for superformat.  Using more cylinders has no effect on the
throughput.

     density     tot. cap.    throughput    media description
     5 1/4 HD    1494KB        27KB/s       hd sect=18 cyl=83
     3 1/2 HD    1743KB        26KB/s       hd sect=21 cyl=83
     3 1/2 ED    3486KB        52KB/s       ed sect=42 cyl=83