Omnibus TSC8-75 schematic?

Paul Anderson useddec at
Thu Oct 29 21:57:57 CDT 2015

Hi Rick,

Call me if you can.

217 766 7690

On 10/28/15, Rick Bensene <rickb at> wrote:
> 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
> unobtainium.
> 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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