BACKUP (MS-DOS)
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.
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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.
Specifications
- Tech docs from FreeDOS
- One could presumably learn about the format(s) from the MS-DOS 4.0 source code, listed below.
