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[by whom?] 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.
^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.