HP portable / HP 110 Service Manual

[Jim Horn]

I believe the 27C256 will drop in and go just fine. Do check the data sheets to be sure. They're available via vendors on the web, though programming them may be a challenge without a device programmer (which is pretty simple for this particular part).

Back in the 1980s lots of folks would pop the ROMs or EPROMs from devices they bought, read their contents, then tweak the code, program ("burn") an EPROM with the results and put that back into the device. Hacking as a positive pursuit has a long history...