The folks at Bell Labs were asked to figure out if Mark Williams had copied Unix directly or via too much knowledge already obtained, or whether it was truly a clean room recreation. I don't remember all the details, but it became clear after a while that it was indeed a reasonably clean rewrite. This was done by looking for corner cases that were an accident of the original implementation and would be unlikely to appear in a version created separately. One detail that did stick with me was the discovery during this process that ppt, the paper tape simulator, mispunched a letter, I think "R", but the Mark Williams version did not. Was that compelling? Not on its own, but it was funny and memorable. -rob On Sun, May 1, 2022 at 9:46 PM Ron Natalie wrote: > Mark Williams Coherent was one I worked with on the PC many years ago. > > > On May 1, 2022, at 11:34, Andrew Warkentin wrote: > > > > What was the first "clone" functional Unix (i.e. an OS not derived > > from genetic Unix code but highly compatible with genetic Unix)? Idris > > is the earliest such OS of which I am aware (at least AFAIK it's not a > > genetic Unix), but was it actually the first? Similarly, which was the > > first "outer Unix-like" system (i.e. one with strong Unix influence > > but significantly incompatible with functional Unix)? Off the top of > > my head the earliest such system I can think of is Thoth (which > > predates Idris by almost 2 years), but again I'm not sure if it was > > actually the first. > >