BACKUP (MS-DOS)

File Format
Name	BACKUP (MS-DOS)
Ontology	Electronic File Formats Backup BACKUP (MS-DOS)
Extension(s)	.@@@, .@02, .001, others

The BACKUP command in MS-DOS backed up the contents of a hard disk to files of a proprietary, undocumented format which could be returned to their original file structure using the RESTORE command.

There are at least two quite different formats:

• The format used by MS-DOS 2.0(?) through 3.2. We'll call it 2.0 format.
• The format used by MS-DOS 3.3 through 5.x. We'll call it 3.3 format.

For the format used by MS-DOS 6.x's MSBACKUP.EXE utility, see Norton Backup.

Format details

Format details - 2.0

Backed up files usually keep their original filenames. The data is modified, to add a header. In case of a duplicate filename (because the same filename appeared in different directories), a replacement extension like .@02 is used. A file may be split into multiple backup files, each containing a fragment of its data.

An extra BACKUPID.@@@ file is written to each disk, containing general information about the backup. It doesn't contain any critical information.

Format details - 3.3

Just two files are written to each floppy disk: CONTROL.001 (or .002, etc.), and BACKUP.001 (.002, etc.). The CONTROL file contains information about the file data in the corresponding BACKUP file.

Identification

Identification - 2.0

BACKUPID.@@@: (TODO)

Data files: It's possible to heuristically identify these files from their contents, but they don't really have any distinctive markings. (TODO)

Identification - 3.3

A CONTROL.* file starts with byte 0x8b, followed by ASCII "BACKUP  " (which ends with two spaces).

The BACKUP.* files can't be identified from their contents, as they contain nothing other than the contents of the backed up files.

Specifications

• Tech docs from FreeDOS
• One could presumably learn about at least one of the formats from the MS-DOS 4.0 source code, listed below.

Software

• MS-DOS, at WinWorld
• MS-DOS 4.0 source code: BACKUP, RESTORE

Sample files

2.0 format:

• dexvert samples — archive/dosBackupFile
• [1] → *.ddi (DiskDupe format) → ...
  • Examples of split files are LNALLMS.BAT from parts 1 and 2, and BTPARSE.EXE from parts 2 and 3.

3.3 format:

• {VOL583.ZIP, VOL584.ZIP} → ...

Links

• Backup command help