My understanding of AIX was that IBM licensed the System V source code and then proceeded to "make it their own". I had a days experience with it on a POS cash register fixing a client issue. The shocker - they changed all the error messages to error codes with a look at the manual requirement.

Not sure if this is true in its entirety or not.
But that's what I recall, thst it was not a from scratch rewrite but more along the lines of other vendor UNIX clones of the time. 
License the source, change the name and then beat it to death.

On Sun, May 1, 2022, 2:08 PM ron minnich <rminnich@gmail.com> wrote:
in terms of rewrites from manuals, while it was not the first, as I
understand it, AIX was an example of "read the manual, write the
code."

Unlike Coherent, it had lots of cases of things not done quite right.
One standout in my mind was mkdir -p, which would return an error if
the full path existed. oops.

But it was pointed out to me that Condor had all kinds of code to
handle AIX being different from just about everything else.


On Sun, May 1, 2022 at 7:12 AM Kenneth Goodwin
<kennethgoodwin56@gmail.com> wrote:
>
> I actually purchased several copies of Coherent when it was first released and used it as printer servers for a bunch of inexpensive Centronics based printers. lpd based server to server transfers. Took the printing burden off the main systems. Someone came out with a network based print spooler box (Milan ??) later on which I switched over to after MW passed into obscurity.
>
>
> On Sun, May 1, 2022, 7:46 AM Ron Natalie <ron@ronnatalie.com> wrote:
>>
>> Mark Williams Coherent was one I worked with on the PC many years ago.
>>
>> > On May 1, 2022, at 11:34, Andrew Warkentin <andreww591@gmail.com> 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.
>>