I've been burning some ROMs for my HP Series 80 machine so whilst I was at it I thought I'd quickly take a backup of the ROM in the HP 9121 drive system.

First issue - there is no part number on the ROM! There is a manufacturer's symbol (AMD) and a date code (wk28/1983) but that's it. Discussing with John at Andromeda Research Labs (where I got my EPROM programmer), he suggested that HP were notorious for not allowing their component suppliers to include part numbers.



Very helpful 30 years! ;)

Anyway, John had some helpful advice - simply assume it's a 27512, read it in, and then check in the buffer where the code repeated: at 0x2000 it's a 2764, 0x4000 it's a 27128, 0x8000 it's a 27256.

Sure enough I could see the code repeated at 0x2000 … meaning it was a 2764 device holding 8KB.

Here's the ROM in the very remote chance someone needs to burn a new one for their HP 9212D disk system.

It is labelled "09121 15510 REV D".