1. What edition of UNIX were they likely to be using?
Already answered ...
2. What versions of "Standard Pascal" were in vogue on UNIX at the
time (1981)?
Remember in 1981, the 'Pascal Standard' was still in flight. ISO 7185 was 1983 and Pascal really does not standardize enough that real portability was possible until the 1990 version and people actually started implementing compilers that obeyed it.
3. What combinations of UNIX/Pascal were popular?
Depends the implementation... there were a number of them... there were the ones I had at that time
- UCB Pascal -- pi being the most popular for the PDP-11, and later pc for the Vax
- VU Pascal for the 11
- The Zurich P4 compiler was around and of course eventually begat UCSD, but I don't remember that it was directly made to run on Unix[I did not have one], although it may/must have been.
- The Similer2 compiler for 68000 [was one of Wirth's -- I think was the basis for the compiler that they used for Lilith - or maybe it was a fork that produced the Lilith and the Similer2 compiler -- I don't remember]. That showed up on a couple of the 68K workstations in 1981.
- Andy's Amsterdam Toolkit
- There was a compiler that the RTS folks had at MIT, but I don't know its origin or how complete it was.
- Purdue had something that had started on the CDCs -- that went to Tektronix and was the basis for some of the stuff the Logical Analizer folks were using. It was cross compiler that ran on Unix and generated 8-bit microprocessor code for embedded systems.
- Per Brinch Hansen had a Pascal that we was pushing, but I don't think he even moved it to Unix
- Plus, the "Tunis" folks in Toronto had a Concurrent-Pascal and a UNIX-like system that ran on PDP-11s.
And the problem was 'standard' - lots of people messed with it and every Pascal was a little different. In 1981 at one of the HP/Tektronix [Hatfield/McCoy parties - Stienhart probably remembers], Mike Zuhl, TW Cook and I counted 14 different "Tek Pascal's" and over 25 "HP Basic's" -- each was a little different.
UCSD Pascal was its own system, not Unix [sort of like Smalltalk -- a walled garden within itself]. They started with the P4 compiler but they made it work on 8-bit systems, so while it was around, it was not a UNIX Pascal >>and<< it the Standard was still in flight. The OMSI Pascal compiler was popular for the PDP-11's, but it was RT-11 and RSX [maybe RSTS, but I'm not sure]. The Zurich PDP-10 Compiler was very popular in PDP-10 land. DEC released the VAX/pascal for VMS, which they eventually brought to Ultrix and Tru64. I believe that that was a scratch rewrite and did not use P4 or anything from the PDP-10s or CDC systems before it.
One of the big issues with P4 based stuff is that the original P2 porting kit from Wirth assumed a 40 bit integer of the CDC system. Making it work with a 36 bit world was a tad easier than the 32 or 16 bit world, much less the 8-bit micros. Folks like DEC, UCB and Amsterdam which started over with a new front end, tended to have an easier go of it and often had better compiler tools [which were mostly C based BTW for UNIX and a combination of Pascal and BLISS at DEC].
Sun later brought the UCB PI and PC to the SunOS, but pls Rob G/Larry correct me here - I think they later did their own compiler when they did their new C and Fortran. Masscomp started with the Similer2 compiler, but eventually did a new front end that matched their C and Fortran like DEC had.
As for SWTinP running with FreePascal. I looked into it and decided it was doable, but never went very fair with my investigation since the need for it, was less. Back in the days of VMS, Pr1meOS and the like, SWT was a Godsend. But Windows and like have real Unix subsystems, so I never really was motivated other than pure curiosity.