In MS-DOS 5.0 and newer, PC-DOS 5.0 and newer, Windows 9x, Windows NT 3.1-2000, and OS/2 4.x, the FORMAT command (present in some form or another in literally every single version of Q/86-/MS-/PC-DOS, Windows, and OS/2 ever) offers the /F switch for choosing what capacity to format a floppy disk to.1
In DOS 5+ and Windows 9x, the description of the /F switch (brought up, along with much other information, by entering
format /? at the command prompt) is as follows:
/F:size Specifies the size of the floppy disk to format (such as 160, 180, 320, 360, 720, 1.2, 1.44, 2.88).
The description of the Windows NT 3.1-4.0 /F switch is (apart from a slight change in wording and the addition of support for 20385-KiB floptical disks) almost identical:
/F:size Specifies the size of the floppy disk to format (160, 180, 320, 360, 720, 1.2, 1.44, 2.88, or 20.8).
Windows 2000’s /F switch has considerably greater functionality:
/F:size Specifies the size of the floppy disk to format (160, 180, 320, 360, 640, 720, 1.2, 1.23, 1.44, 2.88, or 20.8).
The OS/2 /F switch is the simplest of all:
/F:xxxx Specifies the size to which the diskette is to be formatted. For example: 360, 720, 1.2, 1.44, 2.88.
For most of these options, even though the only thing specified is the (approximate) formatted capacity,3 there is no ambiguity as to what size, density, and sideness of floppies they are for:
- 160: 160-KiB (40 tracks per side, 8 sectors per track) single-sided double-density (SSDD) 5.25” floppy
- 180: 180-KiB (40 tps, 9 spt) SSDD 5.25” floppy
- 720: 720-KiB (80 tps, 9 spt) double-sided double-density (DSDD) 3.5” floppy
- 1.2: 1200-KiB (80 tps, 15 spt) double-sided high-density (DSHD) 5.25” floppy
- 1.23: 1232-KiB (77 tps, 8 spt) DSDD 8” floppy4
- 1.44: 1440-KiB (80 tps, 18 spt) DSHD 3.5” floppy
- 2.88: 2880-KiB (80 tps, 36 spt) double-sided extended-density (DSED) 3.5” floppy
- 20.8: 20385-KiB (755 tps, 27 spt) double-sided floptical disk
However, for the remaining three, there are multiple floppy formats with a capacity that fits:
- 320-KiB (40 tps, 8 spt) DSDD 5.25” floppy, or...
- 320-KiB (80 tps, 8 spt) single-sided quad-density (SSQD) 5.25” floppy, or...
- 320-KiB (80 tps, 8 spt) SSDD 3.5” floppy
- 360-KiB (40 tps, 9 spt) DSDD 5.25” floppy, or...
- 360-KiB (80 tps, 9 spt) SSDD 3.5” floppy
- 640-KiB (80 tps, 8 spt) double-sided quad-density (DSQD) 5.25” floppy, or...
- 640-KiB (80 tps, 8 spt) DSDD 3.5” floppy
For each of these three /F options, which of the two (or three, in 320’s case) possible formats is the option intended to produce? Does it change at all, depending on whether the drive holding the floppy disk to be formatted is a 5.25” or a 3.5” drive (distinguishing between DSDD, SSQD, and DSQD 5.25-inchers, on the one hand, and SSDD and DSDD 3.5-inchers, on the other), or maybe on whether the /1 switch (used to tell FORMAT to format only one side of the disk) is used (distinguishing, for 320 and 360,5 between DSDD 5.25-inchers, on the one hand, and SSQD 5.25-inchers and SSDD 3.5-inchers, on the other)?
1: The /F switch is technically still present in every Windows NT version from Windows XP right up through Windows 10, but has been neutered, with only the “1.44” (1440-KiB DSHD 3.5” floppy) option available.2
2: Floppies can still be formatted to other capacities on these systems, assuming that the floppy drive’s firmware supports non-1440-KiB-DSHD-3.5” formats (most internal floppy drives do; most USB floppy drives don’t), but this requires the user to manually enter the number of tracks per side and the number of sectors per track (using the /T and /N switches, respectively), and the support present in earlier NT versions for formatting single-sided disks is, so far as I can tell, completely gone.
3: In contrast, the /F switch for DR-DOS’s FORMAT command explicity states what sizes of disks its various options correspond to; unfortunately, as DR-DOS is a completely independent development (though an essentially-completely-binary-compatible one) from Microsoft and IBM’s offerings, one can in no way assume that the list of floppy formats supported by DR-DOS is exactly the same as that supported by [MS-/PC]-DOS/Windows/OS/2.
4: The capacity of a DSDD 8” floppy is 1232 KiB, rather than the 616 KiB one would expect from the per-disk sector count, because DD 8-inchers use 1024-byte sectors rather than the 512-byters standard on the smaller sizes of floppies. (SD 8-inchers, which are not supported by any FORMAT version of which I am aware, use 128-byte sectors.)
5: It wouldn’t help for 640, as both of the two disk formats with 640-KiB capacity are double-sided.