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Format (command)

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Title: Format (command)  
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Subject: NewDos/80, Disk utility, Diskcomp, Convert (command), Diskcopy
Collection: External Dos Commands, Hard Disk Software
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Format (command)

A component of Microsoft Windows
Also available for DOS, OS/2, Windows 9x

Format, a command-line utility included in Microsoft DOS, IBM OS/2 and Microsoft Windows operating systems, carries out disk formatting.

The command performs the following actions by default on a floppy drive, hard drive, solid-state (USB), or other magnetic medium (it will not perform these actions on optical media):

  1. clearing the FAT entries by changing them to 0x00
  2. clearing the FAT root directory by changing any values found to 0x00[nb 1][1][2][3]
  3. checking each cluster to see if it is good or bad and marking it as good or bad in the FAT

Optionally (by adding the /S, for "system" switch), Format can also install a Volume Boot Record. With this option, Format writes bootstrap code to the first sector of the volume (and possibly elsewhere as well). Format always writes a BIOS Parameter Block to the first sector, with or without the /S option.

Another option (/Q) allows for what Microsoft calls "Quick Format". With this option the command will not perform steps 2 and 3 above. Format /Q does not alter data previously written to the media.

Typing "Format" with no parameters in MS-DOS 3.2 or earlier would automatically, without prompting the user, format the current drive; however in MS-DOS 3.3 and later it would simply produce the error: "required parameter missing".

Any storage device must have its medium structured to be useful. This process is referred to as "creating a filesystem" in Unix, Linux, or BSD. Under these systems the more robust command "mkfs" exists. It creates many kinds of filesystems, including those used by DOS, Windows, and OS/2.


  • See also 1
  • Notes 2
  • References 3
  • External links 4

See also


  1. ^ The directory entries get filled with 0x00 since MS-DOS 1.25 and PC DOS 2.0. If the Format command line option /O is provided, the first byte of each directy entry is set to 0xE5h to create a FAT format useable by PC DOS 1.0-1.1. However, not giving /O will significantly speed up directory searches under MS-DOS 1.25 and PC DOS 2.0 and higher. Older versions of MS-DOS, PC DOS, and 86-DOS only supported the 0xE5 marker.


  1. ^   (NB. While the publishers claim this would be MS-DOS 1.1 and 2.0, it actually is SCP MS-DOS 1.25 and a mixture of Altos MS-DOS 2.11 and TeleVideo PC DOS 2.11.)
  2. ^ Shustek, Len (2014-03-24). "Microsoft MS-DOS early source code". Software Gems: The Computer History Museum Historical Source Code Series. Retrieved 2014-03-29.  (NB. While the author claims this would be MS-DOS 1.1 and 2.0, it actually is SCP MS-DOS 1.25 and a mixture of Altos MS-DOS 2.11 and TeleVideo PC DOS 2.11.)
  3. ^ Levin, Roy (2014-03-25). "Microsoft makes source code for MS-DOS and Word for Windows available to public". Official Microsoft Blog. Retrieved 2014-03-29.  (NB. While the author claims this would be MS-DOS 1.1 and 2.0, it actually is SCP MS-DOS 1.25 and a mixture of Altos MS-DOS 2.11 and TeleVideo PC DOS 2.11.)

External links

  • Microsoft Windows XP Professional Product Documentation: "format"
  • MSKB255867: How to Use the Fdisk Tool and the Format Tool to Partition or Repartition a Hard Disk
  • Microsoft DOS format command
  • Recovery Console format command
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