On Wed, Jun 19, 2019 at 9:23 PM Bob Smith via cctalk
 <cctalk at classiccmp.org> wrote:
  My recollection, Unix on the 11 started with the
20 but because of the
 limited capabilties, it really was done on the /45. 
 The good stuff, yes, but it was still recognizable on the 11/20...
 
https://github.com/jserv/unix-v1
 > unix developed on 11/20 with 20 on panel or
machine that just said pdp/11? 
 Based on comments from Ken Thompson at his keynote at VCF East this
 year, just "PDP-11" (he specifically asked if anyone in the audience
 had ever touched _that_ version, no "/20").
  The three rings or 3 execution levels were not
supported on the
 original machine. 
 Sure but v1/v2 UNIX was a lot simpler than v5.