IBM PC hacking
melamy at earthlink.net
Wed Sep 14 19:04:07 CDT 2005
the original IBM PC Bios was a Motorola 24 pin ROM. In the early
days, I used a 28 pin socket and wired to a 24 pin header to be able
to modify the bios and use a standard 28 pin EPROM for changes. There
were no latches in the ROM. It was probably cheaper for IBM to get a
masked ROM then to use EPROMs which were relatively expensive for the
quantity they were buiding. There was no EPROM equivalent for the
best regards, Steve Thatcher
> > >
> > > > The PC used either EProms, (16K I think) and the Roms that were
> > > > shipped with the BIOS were registered. The standard Data I/O would
> > >
> > > Do you mean there were internal data latches in the IBM ROMs?
> > >
> > Yes, as I understand it and saw, the roms could be enabled, using a
> > line that the data I/O didn't drive (29b variety any did not). So you got
> > FF out when you read them.
>I can believe there were some odd enables on those ROMs, but I wasn't
>aware of any internal latches. I will have a look again.
More information about the cctalk