According to this page that Dennis Ritchie wrote, the
they used was indeed an 11/20 but it was before there were PDP-11 model
And, of course, the PDP-7 Unix development came before the PDP-11 version :)
It states that their 11/20 had a KS-11 memory management unit, was that mandatory for
running v1 Unix on an 11/20?
The 1971 Unix Programmer's Manual mentions their 11/20 had 24 KB (surely KW?) memory
rather than 28KW.
Having recently acquired a 3rd-party 8KW unibus memory module (stack + drivers + control,
all integrated into a
DD-11-sized form) that is the same model and brand as the 16KW unit in my ex-BHP
steelworks FOX 2 (11/15), perhaps
there is the very, very slim hope that if the whole thing works it might be enough to run
v1 someday. That day
however is a long way away, but I think I now have most of the hardware needed.