clearing the FAT root directory by changing any values found to 0x00[nb 1][1][2][3]
checking each cluster to see if it is good or bad and marking it as good or bad in the FAT
Any storage device must have its medium structured to be useful. This process is referred to[by whom?] as "creating a filesystem" in Unix, Linux, or BSD.[4] Under these systems different commands are used. The commands can create many kinds of file systems, including those used by DOS, Windows, and OS/2.
Implementations
FORMAT.COM, among several other commands, in IBM PC DOS 1.0.
On MS-DOS, the command is available in versions 1 and later.[19]
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.[citation needed]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".[citation needed]
DR/Novell DOS
DR DOS 6.0 includes an implementation of the format command.[20]
FreeDOS
The FreeDOS version was developed by Brian E. Reifsnyder and is licensed under the GPL.[21]
ReactOS
The format command on ReactOS
The ReactOS implementation is based on a free clone developed by Mark Russinovich for Sysinternals in 1998. It is licensed under the GPL.[22]
It was adapted to ReactOS by Emanuele Aliberti in 1999 and supports FAT, FAT32, FATX, EXT2, and BtrFS filesystems.
↑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 directory entry is set to 0xE5h to create a FAT format usable by PC DOS 1.0-1.1. However, not providing /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.