Rebirth of IMSAI

From: Richard Erlacher <>
Date: Sun Mar 21 20:07:04 1999

Unfortunately, the adoption of the IEEE696 standard was more or less, the
cause of its demise. Whereas pre-696 board makers went to great lengths to
make their products work with a range of CPU's, memory, FDC's, HDC's, I/O
cards, etc, after the standard was adopted, these manufacturers used the
standard as an excuse to ignore the others in the industry and the result
was that interoperability suffered.

If you want a current-generation computer with a useful front-panel display,
you have to synthesize a single-step operation and dump the internals of the
processor to the display hardware. Too much of the operation is packed
inside the processor IC.

If it's the front-panel you're after, and if you don't mind that the front
panel needs to be shielded to meet FCC standards, as does the cabling you'll
need, else you'll knock out all the broadcast TV reception in your
neighborhood. Once that happens you'll have that ugly FCC van parked across
your driveway. . .

If you're bent on having an S-100 bus, it would work better to use an 8080
than a Z-80, as the S-100 signals were designed around an 8080. Most of the
logic found on typical Z-80 cards for the S-100 is to regenerate those
awkward and not terribly useful signals which Intel, Zilog, and others spent
megabucks to eliminate so they'd be there to make the S-100 go. In this one
respect, and recognizing the fact that hindsight is always 20-20, I'd say
that Multibus-I was designed a lot better for general purpose computing.

If you're really interested in running a "clever/new" S-100, you might try
building a pod with which to emulate the 8080 processor from your PC. Old
Intel documents will provide the desired timing, and I don't really think
you need too fast a PC to emulate the old 8080 in real time. Writing the
code to interpret the 8080 code correctly and produce the appropriate signal
flow will show you definitely understand the workingsof the processor.

You can even build a virtual front panel on your PC's CRT. Additionlly, you
can run a window of "Hyperterminal" to support your need for a terminal with
which to talk to the S-100 box as a console.

I just took a look to see what I've got that would be interesting to
integrate into a system on one of the big S-100 cardcages I've been hoping
someone would take away. I must've hit my head . . .


-----Original Message-----
From: John Ruschmeyer <>
To: Discussion re-collecting of classic computers
Date: Sunday, March 21, 1999 5:51 PM
Subject: Re: Rebirth of IMSAI

>> Why not create a current design for a modern front panel system? ok,
>> styling because I like the silk screening of the 8800b and the 8080 but
>> *some* modern accoutrements while still providing that front panel
>> experience.
>To me, that seems the best compromise between the extremes in this
>Design a state-of-the-art S-100/IEEE-696 box and cardset (Z-80 based)
>including an FDD controller which could use a standard 3.5" drive, offer
>the whole thing as a kit with bundled CP/M (or clone).
>Sort of like the difference between a concours restoration of a Shelby
>Cobra and one of the Cobra kits.
Received on Sun Mar 21 1999 - 20:07:04 GMT

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