I thought Unix was written and used on PDP-11 systems.
It was. So was DOS-11, RT-11, RSTS/E, RSX-11-*, IAS, etc.
Which PDP-11 systems ought I keep an eye out for?
Anything but the very lowest end (11/04, 11/03, etc.) if you want
to run Unix.
While Unixes show up on -11's in many applications, they were
least popular in industrial-control type situations, which is where
most -11's are used. Of course, just to complicate things, they
were using Unix variants on 11-based industrial control systems too!
And you are right, it is indeed possible that this particular 11/23
has some Unix packs in the deal, I'm just pointing out that it's
And you were especially correct that a buyer would be unwise to
ditch the drives and packs. An -11 is more than just the CPU box,
if you want to do anything even vaguely useful/interesting!