2 Oct
2026
2 Oct
'26
1:56 p.m.
On Oct 2, 2026, at 4:38 PM, Martin Eberhard via cctalk
<cctalk(a)classiccmp.org> 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