DEC DW11 information?

Ethan Dicks ethan.dicks at
Mon Feb 27 22:52:34 CST 2017

On Mon, Feb 27, 2017 at 11:32 PM, Josh Dersch <derschjo at> wrote:
> Hi all -
> Anyone have any technical information (manuals, schematics, etc.) for the
> DEC DW11 UNIBUS->QBus interface?  I'm curious to know what it's capable of
> and what the requirements are, especially on the QBus side of things.  What
> kind of backplane is required?  I assume it doesn't support 22-bit QBus
> devices given the age of the interface (and the complexity required to do
> so), but does it handle 18-bit devices, or only 16?

I saw one in a PDP-11/34 at a Physics Lab at Ohio state in the early
1990s.  It was in there so that they could use an IBV11 IEEE-488
interface with a Unibus machine.  AFAIK, it's 18-bit not 16-bit.
22-bit Qbus wouldn't be directly controllable from a Unibus anyway
(machines like the 11/44 that can address more than 256MB of memory
have Unibus mapping registers that take care of RAM addressing, but
the Unibus is still always 18-bit).  The DW-11 came with a 4-slot hex
Qbus backplane, a DDV11-CK, I'm fairly certain it was, that mounted
directly in the BA11-K box, right next to a DD11-DK and a DD11-PK that
were the Unibus slots for the CPU and memory.

I've always wanted to see if it would work with a Qbus SCSI controller
since Unibus SCSI controllers are far, far less common.


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