MSCP - was Re: Unibus / Qbus

Paul Koning paulkoning at
Sun Oct 23 13:16:24 CDT 2016

> On Oct 22, 2016, at 6:05 PM, Toby Thain <toby at> wrote:
> On 2016-10-22 4:08 PM, allison wrote:
>> ...
>> FYI I have never heard of any one recreating the RQDX1/2/3 software
>> protocol MSCP
>> as it was nontrivial, proprietary, and copyrighted.
> It's been implemented in simh, afaik. Its reputation is a little more imposing than the reality.

Well, it certainly is vastly more complex than the older CSR-based controllers.  That's not to say it's undoable; compared to, say, SCSI it's not that painful.  (In fact, you might say it's a natural predecessor of SCSI.)  Proprietary, yes.  Copyrighted?  perhaps so, but copyright is irrelevant if you want to build implementations.  (It only matters if you want to make copies of the document.)  I assume MSCP was patented, but any patents have expired long ago so those aren't relevant any longer either.  

The main question is whether a sufficiently accurate spec is available.  In the case of MSCP (and TMSCP, which is a close relative) the answer is yes (on Bitsavers).  And unlike some other standards sources, DEC standards generally are written to the level of quality that conformance implies interoperability -- in other words, do what the spec says and it will work correctly.


More information about the cctalk mailing list