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Format \windows\system32\format.com

Prepare floppy diskettes , hard disks, and some removable media for use.

To Open

Command Prompt format.com


format volume [/q] [/c] [/x] [/v:label] [/fs:file-system] [/a:size]


Before data can be stored on a floppy disk, hard disk, or many removable media disks (like Zip disks), the disk must be formatted. This process creates various low-level data structures on the disk, such as the filesystem (FAT, FAT32, NTFS, etc.). It also tests the disk surface for errors and stores bad sectors in a table that will keep them from being used. If there’s any data on the disk, it will be erased.

The options for Format are:


The drive letter, followed by a colon, containing the media to be formatted. For example, to format the floppy in drive A:, type:

format a:

If the specified drive is a hard disk, you’ll be prompted to verify that you actually want to erase the disk.


Performs a “quick” format, a process that only wipes out the file table, resulting in an empty disk. This option does not check for bad sectors, nor does it rewrite the filesystem. Also, it does not write over data on the disk, meaning that files could potentially be recovered or “undeleted.” The advantage of the /q option is that you can erase a disk in a few seconds.


Files created on the new volume are compressed by default (NTFS volumes only).


Forces the volume to dismount first, if necessary. All opened handles to the volume would no longer be valid. This effectively disconnects the drive from Explorer and all other programs, closing any open files stored on the drive, before any changes are made.

/v :label

Specifies the volume label, an arbitrary title you assign to any disk. It can be up to 11 characters and can include spaces. The volume label will show up next to the drive icons in Explorer (hard disks only) and at the top of dir listings (see Appendix C). See “Label”, later in this chapter, for more information. If the /v option is omitted, or the label isn’t specified, a prompt for a volume label is displayed after the formatting is completed. If a label is specified with /v and more than one disk is formatted in a session, all disks will be given the same volume label.

/f :size

Specifies the size of the floppy disk to format (such as 160, 180, 320, 360, 720, 1.2, 1.44, 2.88). format size (specified with the /f option) must be equal to or less than the capacity of the disk drive containing the disk to be formatted. For example, a 1.44 MB capacity drive will format a 720K disk, but a 720K drive will not format a 1.44 MB disk.

/fs :filesystem

Specifies the type of the filesystem; can be fat, fat32, or ntfs.

/a :size

Overrides the default allocation unit size, which, when multiplied by the number of clusters, equals the final capacity of the disk. Allowed values for size depend on the filesystem:

  • NTFS supports 512, 1024, 2048, 4096, 8192, 16K, 32K, and 64K.

  • FAT and FAT32 supports 512, 1024, 2048, 4096, 8192, 16K, 32K, 64K, (and 128K and 256K for sector size > 512 bytes).

  • Note that the FAT and FAT32 filesystems impose the following restrictions on the number of clusters on a volume:

  • FAT: Number of clusters <= 65,526

  • FAT32: 65,526 < Number of clusters < 4,177,918

  • NTFS compression is not supported for allocation unit sizes above 4096.


  • The /f, /t, and /n parameters are also available for use with Format, but are essentially obsolete. Type format/? for more information.

  • If formatting an ordinary 3.5” floppy diskette, the disk will always be formatted to a capacity of 1.44 MB. The DMF diskette format, which squeezes about 1.7 MB on a standard floppy, is not directly supported by Format. If formatting a pre-formatted DMF diskette, use the /q parameter to preserve the format and only erase the files. To create new DMF diskettes, you’ll need the WinImage utility (Version 2.2 or later), which can be downloaded from http://www.annoyances.org.

  • The easiest way to format a disk is to right-click on the drive icon in Explorer or My Computer and select Format. However, using Format from the command line is more flexible, and in some cases, faster.

See Also

“FAT to NTFS Conversion Utility”, “Label”

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