IBM PC hacking

[jim stephens]

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
was not.

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.

>
> -tony