ID-ing a PC backup format

[Chuck Guzis]

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.

--Chuck