Modcomp Computer?

CRC technobug at
Wed Aug 31 02:24:26 CDT 2005

On Tue, 30 Aug 2005 16:07:04 -0700 (PDT), Jeff Davis"  
<jdaviscl2 at> wrote:

> The color scheme was brown and white, titled "Modular Computer
> Systems", with a ModComp logo.

What you found was a Modcomp II, a 16-bitter with 64 kwords of  
memory. The machine was modeled (ala SEL) on the IBM 1800 series  
controllers and were used primarily in communications and process  
control. There were produced in the 1974-78 period, or thereabouts.  
The design was interesting in that it used microcode which could be  
extended through a microword bus. Consequently, unused instructions  
were used for floating point, communications controllers, etc. OS was  
multi-tasked, priortized, and fully pre-emptive. The file system was  
ala IBM: you allocated your files at sysgen time. They were quick  
machines for the time.

> The insides were odd - instead of the usual card cages, a lever let  
> you pull
> out a sliding tray with (very rough est.) 15 x 15 inch cards that  
> were mounted
> on an accordian style fold-out bracket, which I couldn't figure out  
> how to
> fold out.

There is a knob on top of each plane which when pulled up allows the  
plane to swing open. By far the easiest computer to work on I've run  

> They were interconnected with various flat cables.  The outside
> most card was wire-wrapped, I couldn't see much of the other cards  
> but I got
> the card names and part#s of all of them:
> 1 of Loop Controller, 551-100169-001
> 1 of MC II Plane I, 551-100140-001
> 1 of MC II Plane I, 551-100140-001
> 4 of 16K memory, 551-100069-001

IIRC all the planes, with the exception of the memory were wire- 
wrapped and all ICs are socketed. What makes these planes unique is  
that the power regulation is at the top on each plane. Raw DC is  
provided from some honkin' supplies located at the back of the  
drawer. The original IIs were implemented in 74Hxx (read very hot,  
but not too fast) and consequently there are IIRC 9 fans on the  
bottom of the drawer.

Generally, I/O was housed in plain boxes beneith/along side the  
computer, but constructed with the same planes as the main computer.  
However, these planes were oriented horizontally.

I ran one in an experiment during the period 1975-78. It was mounted  
in a trailer which traveled over 10k miles over the period of the  
experiment - damn reliable beast.

> Anyone know what this is?  If anyone wants it, it's located in  
> Santa Barbara,
> California - email me and I can give you the contact info for the  
> surplus
> department there (or google "surplus ucsb").  I'll try to get out  
> there on
> thursday and take some pictures if anyone is interested.
> Jeff

I would love to see some pictures :-))


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