Interesting formats
*******************

This table lists a few interesting formats.  Some of them are not included in the table of predefined formats due to lack of space.  You may use these by setting the geometry of the variable geometry device using setfdprm.  Most of the entries in the following table do not describe a single format, but rather a family of formats which share a common characteristic.  For this reason, no precise parameters are included.

80/90/160/180 KB 5.25"
     Original IBM PC, CP/M, Apple II, TRS-80, etc.  Single density, FM (not MFM), 40-track.  Some systems also used "hard" sectoring, with an index hole for each sector.  These are probably readable on standard FDCs if anyone cares to go to the effort.  160KB/180KB formats were double-sided.

320 KB 5.25"
     CP/M, Zenith Z-100, some forms of MS-DOS.  8-sector DD 40-track.

400 KB 5.25"
     AT&T 7300/3B1: cpio format, 10 sectors, DS, 40 tracks.

     PC: MS-DOS, 10 sectors, DS, 40 tracks; formatted by various utilities; readable by some versions of MS-DOS.

<720KB 3.5" formats

       * Some dedicated word-processing systems use lower than normal capacity floppies (some may be 40-track either via "stretching" or by having odd drives; others may be single-sided or use fewer sectors per track, or use "single density" or FM).

       * Atari ST 360 KB floppies: these are 9 sector 250kb/s 80-track single-sided, using a slightly incompatible MS-DOS-like FAT.  Very common distribution format for Atari ST software.

       * Mac 400 KB: single-sided 80-tracks, Mac MFS or HFS file system, Group Code Recording, zone bit recording, variable RPMs from 300 to 600 in 5 zones, and auto-eject mechanism.  Impossible to read on normal PC drives without some form of hardware assistance.

720 KB 3.5"

       * PC: 9 sectors, DS, 80-track; very common.

       * Atari ST: same as Atari ST 360 KB except double-sided.

720 KB 5.25"
     "Quad Density": 9 sectors, DS, 80-track; name is rather misleading, as it is double density 80 track.

800 KB

       * PC: 10 sectors, DS, 80 tracks; readable by MS-DOS; formatted by many PC utilities; "almost standard".

       * Atari ST "Twister": 10 sectors, DS, 80-track; slightly incompatible MS-DOS-like FAT; sector skewing (originated by David Small).

       * Mac 800 KB: same as Mac 400KB except double-sided.

880 KB

       * PC: 11 sectors, DS, 80 tracks, interleaved(?).  Formatted by various PD utilities such as fdformat.

       * Amiga: uses "single-sector" tracks the size of 11 sectors; DS; 80 tracks.  Written by a custom chip rather than a standard FDC; it is very difficult to access these using a standard FDC, though it might be possible in theory, using some trickery.

880 KB - 960 KB
     Atari ST: 11/12 sectors, DS, 80-track, interleaved(?); not very reliable, formatted by various PD utilities.

960 KB
     2m and Linux; 6 sectors interleaved(?), DS, 250kb/s?, 80-track, 1K sectors(?).

1001 KB
     "Japanese" format: 300kb/s, 77 tracks, HD drives/disks.

1040 KB
     2m and Linux only; 13 sectors, DS, 300kb/s, 80-track.

1120 KB
     2m and Linux only; 14 sectors interleaved, DS, 300kb/s, 80-track.  Can only be formatted on Linux; even on Linux, it is difficult to format these on an ED drive.

1200 KB 5.25" HD
     "AT": 360 rpm 500kb/s 80-track 15-sector MS-DOS.

1360 KB 5.25" HD
     Highest "fdformat" noninterleaved 5.25" format.  360 rpm 500kb/s 17-sector MS-DOS.

1440 KB 5.25" HD
     Interleaved 18-sector 360 rpm 500kb/s; highest "fdformat" 5.25" format. 18-sector MS-DOS.

     2m and Linux only: noninterleaved 1024-byte sector 18-sector-equivalent 360 rpm 500kb/s; 18-sector MS-DOS.  A good substitute for 1.44MB 3.5" floppies.

1600 KB 5.25" HD
     2m and Linux only: interleaved?  500kb/s 80-track; 1 8KB sector, 1 2KB sector?

1760 KB 3.5" HD
     2m and Linux only: 11 1KB sectors; 500kb/s, noninterleaved?

1840 KB 3.5" HD
     2m and Linux only: 23-sector equivalent; 500kb/s, noninterleaved.

1920 KB 3.5" HD
     2m and Linux only: 3 4KB sectors; 500kb/s, interleaved?

     2m and Linux only: 1 8KB sector, 1 4KB sector; 500kb/s, interleaved?

2880 KB 3.5" ED
     "Extra Density" or "Extra High Density".   1 Mb/s, 36-sector, DS, 80- track.

3200 KB 3.5" ED
     Non-interleaved, 80 track, 40-sector 1 Mb/s.  Highest capacity that MS-DOS can read directly(?)

3520 KB 3.5" ED
     2m and Linux only: 1 16KB sector, 1 4KB sector, 1 2KB sector? Non-interleaved, 80 track 1 Mb/s.  Highest capacity that 2m can format.

3840 KB 3.5" ED
     2m and Linux only: 1 16KB sector, 1 8KB sector (or is it 3 8KB sectors?).  Non-interleaved, 80 track 1 Mb/s.  Formatted only by Linux, but readable and writeable by 2m.

Linux is able to read almost any MFM disk. These include many CP/M disks and also Commodore 1581 disks. Please get Michael Haardt's documentation on floppy drives for a detailed description of those formats. This can be ftp'ed from the following location:

     ftp://cantor.informatik.rwth-aachen.de/pub/linux/floppy.ps

Commodore 1581 disks are not yet described in this documentation.  Use setfdprm /dev/fd0 DD DS sect=10 cyl=80 swapsides. If you want to use these disks often, redefine one of the "default" formats to be Commodore 1581, and then put it into the autodetection list for the drive. The following example describes how to redefine format number 31 (minor device number 124) to be Commodore 1581:

     mknod /dev/fd0cbm1581 b 2 124
     setfdprm /dev/fd0cbm1581 DD DS sect=10 cyl=80 swapsides
     floppycontrol --autodetect /dev/fd0 31,7,8,4,25,28,22,21

The two latter commands have to be issued after each reboot, so I suggest you put them into your /etc/rc files if you use many Commodore 1581 disks.