Restoring old DOS backups in 2023

• 28 April 2023
• archiving,
• dos,
• til

Recently, as part of an ongoing effort to preserve old work, and to free up physical storage space, I went through the process of imaging all my 3.5-inch floppy disks. I’ve been using my Kryoflux board to save off a .img file for each floppy.

While most of the disks contained .zip files, or multi-disk .zip archives (something for another post), there were several multi-disk backup sets created by some version of DOS Backup in the mid-nineties.

Each of these backup disks contained a single file with names like KK50306D.001. Looking at these files in a hex editor, we can see that they contain the string NORTON Ver 1E in their header. Apparently Microsoft licensed Norton Backup for inclusion in versions of DOS at around that time.

I fondly imagined that someone had written an open source tool for restoring these; I didn’t find one. I briefly thought about doing that myself.

Here are the steps I ended up taking to restore my backup sets:

• It looked as though the only option was using the original DOS restore functionality. But which version of DOS?

• Research led to DOS 6, 6.2, or 6.22 (see DoubleSpace vs DriveSpace and the Stac Electronics patent).

• I installed DOS 6.22 in a VirtualBox VM and tried its version of msbackup. It couldn’t reconstruct the catalog from my disk images.

• Some mucking around and it reconstructed the catalog from specially-named directories on disk, but when I tried to restore, it skipped all the files without explaining why.

• So I installed Windows 3.11 and tried the Windows version of backup, mwbackup.

• mwbackup told me that this backup was made by DOS 6 or 6.20, and pointed me to the DOS readme file, which explained that I could install the DOS 6 or 6.20 versions of msbackup over the 6.22 ones.

• After accidentally trashing my VM, I rebuilt DOS 6.22 and installed the DOS 6 msbackup over the top.

• This version was happy to reconstruct the catalog from floppy images, and I was able to restore all my backup sets.

• The backups include the drive letter that the original files were backed up from. You can choose to restore to a different drive letter, however msbackup will prompt with an "Are you sure?" message for each new directory it needs to create. To avoid that, I used the DOS subst command to map my drive as the drive letter from the original backups, then picked the msbackup option to restore to the original drive letter.

Some links which helped me through this:

• Restoring a Norton Version 1E floppy backup

• Norton Backup for Win3.X

• Win9x & XP MSBackUp File Format and Data Recovery

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