Omnibus TSC8-75 schematic?

Rick Bensene rickb at
Wed Oct 28 18:58:12 CDT 2015

While there are documents out there that describe the function of the
Educomp/Quodata TSC8-75 Timeshare System Controller for Omnibus PDP 8
machines, I have searched high and low, and there doesn't seem to be
/any/ schematics for it anywhere.

I know this was a proprietary board that did some pretty interesting
things to trap IOT, JMP, JSR, and HLT/OSR instructions on the PDP
8/e/f/m/a machines and provide additional capabilities versus DEC's
Memory Extension and Timeshare Control board.   

I have a fantasy of being able to run ETOS on real PDP 8/e hardware, but
I don't have one of these boards, and they seem to be pretty much

There are a few of them out there, but obviously, the owners of these
aren't in the mood to submit them for reverse engineering.   Perhaps
someone out there has already done this, or someone has documentation on
the board that may include schematics that simply hasn't scanned it yet.
Bitsavers comes up with nothing under the DEC archives, and there's no
sign of Quodata or Educomp folders.

I have read the descriptions of the function of the board, and the IOTs
that make it do its things, but I just don't have the expertise on the
guts of the Omnibus PDP 8 machines to be able to take this information
and create a design for a board that performs these functions.  I've
also looked at the code in SimH that emulates the functionality of the
board, but again, it isn't enough information for me to be able to
figure out how to implement it in hardware.

In any case, I think it'd be interesting to see if one of these boards
could be reproduced.

I've found some old ClassicCMP list archives that mention some stuff
about ETOS documentation and folks that worked for Educomp/Quodata that
were involved in the creation of ETOS and this board, but the thread
died over 10 years ago.

I am probably wishing for something that doesn't exist, but I figured
I'd ask anyway, as maybe someone has stumbled across some of this stuff
and just hasn't made it public yet.

Rick Bensene
The Old Calculator Museum

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