IMSAI News?

From: Richard Erlacher <edick_at_idcomm.com>
Date: Sat Jun 15 23:01:19 2002

While it does make sense to put a cheap short mono card or the like in an
S-100 box, together with a simple interface to a PC Keyboard, which is pretty
cheap, the objective being to avoid the extreme expense of a dedicated
terminal, or a PC used as one, I find the whole business of making a PC live
on the S-100 silly, since a PC can simulate a CP/M environment at 50-100x the
speed of the original with no trouble at all. If you have to hack the working
original gear just to run it in the new box, I doubt it's worth it.

More below ...

Dick

----- Original Message -----
From: "Tim Shoppa" <classiccmp_at_trailing-edge.com>
To: <cctalk_at_classiccmp.org>
Sent: Saturday, June 15, 2002 9:03 PM
Subject: Re: IMSAI News?


> > > > This last bit was really problematic becuse the Z800 cannot execute
the
> > > > VGA bios code
> > > > in the ISA board's rom.
> > >
> > > Can't you get a VGA card where the registers are documented well enough
> > > to at least put the think into a simple text/graphics mode without using
> > > the BIOS ROM code? In other words, ignore the ROM and hit the hardware
> > > directly from the Z80? I know I'd have tried soemthing like that if I'd
> > > _had_ to use a VGA card with a CP/M machine...
> > >
If you did that for every operation that required it, you'd be looking at a 1
Hz PC. The Z80 is probably a mite faster than the old 4.77 MHz 8088, but it
would have to go some to match the already slow speed of the 6 MHz PC/AT in
operations like running a VGA.
>
> > The obvious solution, here, is to get a mono card. CP/M software didn't
> > support graphics unless the graphics were associated with a specific
display
> > adapter anyway, so the use of a mono card, particularly one of the "short"
> > mono cards with two serial ports and parallel port on it would probably be
> > just the thing.
>
> In the 80's Compupro sold a S-100 card called "PC Video" which was a
> IEEE696 implementation of the IBM-PC video card. That way you could run
> code on a Compupro S-100 8088 (or 80286) box which actually hit the
> video hardware directly and it would work just like a PC-clone.
>
Unfortunately, the S-100 attempts to emulate the functions of a PC were sadly
inadequate and actually cost a mite more than the same hardware on a PC. The
stuff that worked "just like a PC-Clone" didn't work as fast, since the
business of generating timing adequate to the task ran the S-100 at speeds
considerably slower than the PC/AT. The one useful thing that the '696
standard could have done for us was to relieve us of the burden of having to
generate the i8080 signals that were initially put on the bus by folks not
intending to make a "real" computer out of the system. They still left in the
old phase-1 clock and Sync, together with those stupid, and in some cases,
redundant, status signals that simply allowed the slipshod designer to do
things wrong in a wider range of ways. Once the 8080 was no longer a player,
they should probably have gone with a signal subset that looked more like the
signals on the Multibus-I, which, BTW, looked a lot like the ISA in several
meaningful ways.
>
> It is strangely relevant to the current thread that in the 80's there
> were manufacturers trying to make a S-100 box work like a PC-clone; today
> there are manufacturers trying to make a PC-clone work like a S-100 box.
> Both seem like unnatural acts to me.
>
They were just attempts to get between a fool and his sheckels ...
Received on Sat Jun 15 2002 - 23:01:19 BST