Information on MS-DOS FORMAT, UNFORMAT, and MIRROR Utilities (69767)

The information in this article applies to:
    Microsoft MS-DOS operating system 5.0
    Microsoft MS-DOS operating system 5.0a
    Microsoft MS-DOS operating system 6.0
    Microsoft MS-DOS operating system 6.2
    Microsoft MS-DOS operating system 6.21
    Microsoft MS-DOS operating system 6.22

This article was previously published under Q69767


The following is a brief explanation of the MS-DOS FORMAT, UNFORMAT, and MIRROR commands and how these three utilities interact with one another.

NOTE: MIRROR does not come with Microsoft MS-DOS 6.0, 6.2, or 6.21.


When you format a floppy disk in MS-DOS, the FORMAT command has a built-in feature that creates an image of the system area of the disk. This file contains a copy of the disk's boot sector, file allocation table (FAT), and root directory.

WARNING: If insufficient space is available on the disk to create this file, the UNFORMAT information will not be saved.

This information is intended to be used for recovering from accidental formats. UNFORMATting should be done as soon as possible after the accidental format because each subsequent write to the disk reduces the likelihood of a successful recovery.

The process of creating this UNFORMAT information is identical to running the MIRROR program on the disk. If MIRROR has been run prior to executing the FORMAT command, both images are saved (once again, space permitting), and the UNFORMAT command will give you the option of choosing the MIRROR save file to use for rebuilding. (Your options will be the LAST MIRROR image created or the PRIOR MIRROR image created.) MIRROR files retain their location on the disk even during the formatting procedure.

MIRROR tracks the image file with a control file (MIRORSAV.FIL). If no MIRROR control file can be located on a disk, UNFORMAT scans the disk for a MIRROR image file (MIRROR.FIL). If an image file cannot be located, UNFORMAT scans the disk for old subdirectories. Any subdirectories that are located are attached to the disk's root directory and given a name such as SUBDIR.1, SUBDIR.2, and so forth. The files within these subdirectories may remain intact. (This is a last-resort recovery technique.)

When you format a disk using the /u switch, or if you perform a format that changes the size of the disk, all information on the disk is erased. In cases such as these, no UNFORMAT information is saved, and any MIRROR control/image files that were on the disk are erased. As a result, it is not possible to UNFORMAT this disk.

For specific information on using the FORMAT, UNFORMAT, and MIRROR commands, please see your printed MS-DOS documentation or MS-DOS Help.

Modification Type: Major Last Reviewed: 5/10/2003
Keywords: KB69767