> On Oct 2, 2026, at 4:38 PM, Martin Eberhard via cctalk
> <[email protected]> wrote:
>
> I just finished scanning the DEC documentation for the KH11-A "NPR
> Expansion" option for the PDP11/20 and the PDP11/05 machines. (I just
> bought this drawing set on eBay...)
The 1975 option/module list says it's for the KA-11 and KC-11, which are the
11/20 and 11/15 CPU respectively. Not 11/05, that is an entirely different
design.
> As far as I can tell, this is the only documentation for this CPU
> modification that's online - aside of course for my own reverse-engineering
> drawings from earlier this year.
>
> You can find the drawings here.
> <https://deramp.com/downloads/mfe_archive/011-Digital%20Equipment%20Corporation/08%20PDP-11/05%20Unibus%20Options/KH11-A%20NPR%20Expansion%20Option/>
Wow. I've never heard of this. The O/M list shows it as a regular product,
not a CSS special which was my first guess. I wonder how many they actually
sold. The 11/20 I used in college was a rather large system (it had 16 serial
lines, each requiring a KL11 or DL11 single line serial interface module) plus
RK11, RF11, and TC11. So I'm sure it had one or two bus extenders, but as far
as DMA load is concerned it probably wasn't too crazy. Though the RK11 is
pretty fast for an 11/20 to keep up with (faster, in transfer rate, than the
RF11).
For all I know it may have had one of these, but I never heard that.
paul
