I've got a set of mystery 5.25" DD floppies that appear to be a backup of some sort. [...]

The start of the first sector of the first floppy looks like this:

000000 50 43 42 41 43 4B 55 50-2E 01 00 50 43 42 00 06

000090 9A 01 00 1E 00 01 00 54-55 52 42 4F 43 5C 00 00

Note that it starts off with 'PCBACKUP'. This doesn't seem to match anything in my library. Anyone got any ideas.

I've got a set of mystery 5.25" DD floppies that appear to be a backup of some sort. 10 x 512 byte sectors per track, 40 cylinders, double-sided. Normal sector IDs (Side 0: 0/ Side 1: 1), 1-10. No, it's not FASTBACK nor does it appear to be Central Point's PC Backup. The start of the first sector of the first floppy looks like this: 000000 50 43 42 41 43 4B 55 50-2E 01 00 50 43 42 00 06 000010 04 00 69 00 00 00 00 00-00 00 00 00 00 00 00 00 000020 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 000030 00 00 00 00 00 00 00 00-00 00 00 00 01 01 01 01 000040 01 01 01 01 01 01 01 01-01 01 01 01 01 01 01 01 000050 01 01 01 01 01 01 01 01-01 01 01 01 01 01 01 01 000060 01 01 01 01 01 5A 5A 5A-5A 5A 5A 5A 5A 5A 5A 5A 000070 5A 5A 5A 5A 5A 5A 5A 5A-5A 5A 5A 5A 5A 5A 5A 5A 000080 5A 5A 5A 5A 5A 5A 5A 5A-5A 5A 5A 5A 5A 52 13 C5 000090 9A 01 00 1E 00 01 00 54-55 52 42 4F 43 5C 00 00 Note that it starts off with 'PCBACKUP'. This doesn't seem to match anything in my library. Anyone got any ideas. Oh yeah, this would be circa 1989 or so.