FORMAT.COM is an external MS-DOS command, located by default in %winbootdir%\COMMAND (default is C:\WINDOWS\COMMAND) [Windows 95/98/ME, a.k.a. MS-DOS 7.00/7.10/8.00] or in the MS-DOS 6.xx directory (default is C:\DOS or C:\MSDOS) [MS-DOS 6.00 - 6.22].
    IMPORTANT: To become familiar with the FORMAT.COM command line switches (the documented ones anyway), run one of these commands from any DOS prompt:
    FORMAT /?
    to display the FORMAT.COM help screen.
    NOTE: FORMAT drive: /Q (documented switch) performs a QUICK format ONLY IF the respective drive/partition is already formatted.

  1. FORMAT /AUTOTEST [MS-DOS 5.00 and above ONLY]

    FORMAT /AUTOTEST checks for the existing format of your disk, unless the /U (UNCONDITIONAL) parameter is also used, and then proceeds with an UNATTENDED DISK(ETTE) FORMAT:

    • DOES NOT prompt for a volume label!
    • DOES NOT prompt to format another disk(ette)!
    • NO delay: NO user intervention!
    • Ends WITHOUT pausing!
    After completion, it DOES display disk space statistics, ONLY IF using MS-DOS 5.00/6.xx.
    WARNING: This works on BOTH hard and floppy drives!

  2. FORMAT drive: /BACKUP [MS-DOS 5.00 and above ONLY]

    FORMAT drive: /BACKUP works exactly like /AUTOTEST, applies ONLY to floppy diskettes, but it DOES prompt the user for a volume label, and it DOES display disk space information upon completion.

  3. FORMAT drive: /SELECT [MS-DOS 5.00 and above ONLY]

    FORMAT drive: /SELECT is similar to using the MIRROR command [a MS-DOS 5.00 and earlier ONLY utility, removed from all MS-DOS releases beginning with 6.00], and reads the disk(ette) system area (sector 0).
    In MS-DOS 4.0 FORMAT /SELECT has the same effect as FORMAT /BACKUP.
    [Thank you William!]

  4. FORMAT drive: /U [MS-DOS 5.00 and above ONLY]

    FORMAT drive: /U performs an UNCONDITIONAL format, which DESTROYS every byte of data on ANY hard disk/floppy by overwriting it with zeroes (hex F6h).
    WARNING: ANY disk(ette) formatted using /U canNOT be UNFORMATTED!

  5. FORMAT drive: /SELECT /U [MS-DOS 5.00 and above ONLY]

    FORMAT drive: /SELECT /U makes a disk(ette) UNREADABLE by filling the system area (sector 0) with zeroes (hex F6h), due to using these two incompatible options together. All other sectors are left intact.
    [Thank you William!]
    WARNING: NEVER use these two FORMAT switches TOGETHER on ANY drive!

  6. FORMAT drive: /Z:n [Windows 95B OSR 2.0 + MS-DOS 7.10 and above ONLY]

    FORMAT drive: /Z:n formats a FAT32 drive with a cluster size of n times 512 Bytes.
    drive: = your hard drive letter: C:, D:, E:... etc.
    n = number of sectors per cluster multiplied by 512 (cluster size in Bytes).
    n = 1 creates a 512 Bytes cluster;
    n = 2 creates a 1024 Bytes (1 KB) cluster;
    n = ? creates a ? x 512 = ???? Bytes (???? Bytes : 1024 = ? KB) cluster.
    You can modify the size of the allocation units (sectors) on a FAT32 drive to your heart desire.
    WARNING: It is NOT recommended to change the default cluster size, because some programs such as disk-repair/anti-virus tools may STOP working properly!