Ok guys - I found this while rummaging through stuff I shifted. It's an 8MB .jpg, so I'll only link it - maximum res for anyone keen to try and work out what it is.8 MB image
From memory it plugged into a 5.25 floppy bus, but I can't remember what it does. Might be an early form of copyright protection - a bit of overkill for a dongle!
Copyright 1988/89 on the board and EEPROM. I was working for a Government department back then, and they did introduce automated PABX response - it may
be been a hardware dongle required for the initial version of the software which became redundant at later releases. Ran under C(oncurrent)-DOS, a multi tasking version of DOS. May have moved on to OS/2 in later incarnations, and that may be where this became redundant.
Or I could be misremembering entirely, and it could be off a dedicated PC system for GPS, Radar or Comms. It must have seemed like something at the time that didn't deserve the skip.
At best I can ping the EEPROM off and repurpose it - but if anyone knows what it may be, and if it's useful, send a PM and I'll pass it on.