IBM PC hacking
jwstephens at msm.umr.edu
Tue Sep 13 19:45:53 CDT 2005
Tony Duell wrote:
> > I remember a little shop here in Santa Ana which had the first clone of
> > the IBM PC. It was a single board which had 640k memory, allowed
> > using 64k memories, instead of the 16K memory that the PC and XT
> > earlier models used.
> DId any IBM PC/ST motherboards use 16K DRAMs. Yes, I know the standard
> memory mapping PROM could be set up to use 4 rows of 4816s (64K o nthe
> mainboard), but did IBM ever do that? There's no mention of it in my TechRef.
You may be right, I think due to fog bank between ears that it was 16k in
apple ][ then 64k in original xt, then 256k in the superboard.
> > 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.
> > not read them since they were not programmable, and needed their
> > output enabled to read the data.
> > But once someone had them in the 2716's, it was easy to get them
> > running in your superboard.
> Surely it was trivial to use DEBUG or similar to dump the appropriate
> area of memory to disk...
Yes the dump was trivial, but the R232 or other to an eprom programmer
I had no RS232 or computer driven eprom programmer till much later
when the Taiwanese programmer boards came out.
Before that, I had only Data I/O 29b. Most distributors that you could
buy parts from and beg the use of a programmer could not get the data
into their programmers. So you carried the master parts and programmed
blanks. anything else was a pain.
I'm not talking about what you could do as a company with a budget. I'm
talking about what you could do in your house when Data I/O was getting
around $20000 for programmers, and $4000 for updates, and they
were about all that there was out there.
> > First systems had a 63 watt P/S, and IBM cards if you could find
> > them for video. Also there was no floppy controller on the first
> > board.
> AFAIK, no IBM PC, PC/XT, PC/XT-286, PC/AT, or PC-jr had a floppy (or hard
> disk) contorller on the mainboard. None had parallel ports either, and
> the PC-jr was the only one to have video and a serial port on the mainboard.
The next rev of the superboard had floppy and serial on board. First versions
just cloned the PC motherboard, including the tape interface, later deleted,
and accomodated a full 640k w/o extra boards.
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