was a specific implementation of the programming language Pascal
which used the p-Code machine
Notable was the introduction of separately compilable Units and a String type. Both of which influenced the design of the language Ada programming language.
The UCSD Pascal compiler was distributed as part of a portable operating system, the p-System.
There were four versions of UCSD p-Code engine (p-Code incompatible) each with several revisions of the p-System (and UCSD Pascal); represented with the leading Roman Numeral; operating system revisions were enumerated as the "dot" number following the p-Code Roman Numeral. vis: II.3 represented the third revision of the p-System running on the second revision of the p-Machine.
Original version, never officially distributed outside of the University of California, San Diego. However the Pascal sources for both Versions I.3 and I.5 were freely exchanged between interested users. Specifically the patch revision I.5a was known to be one of the most stable.
Widely distributed, available on many early microcomputers.
Custom version written for Western Digital
to run on their Pascal Micro-Engine microcomputer.
Commercial version, developed and sold by Sof-tech. Did not sell well due to combination of their pricing structure, performance problems due to p-Code interpreter, and competition with native operating systems (which it often ran on top of). After Sof-tech droppped the product it was picked up by Pecan Systems (a relatively small company formed of p-System users and fans). Sales revived somewhat, due mostly to Pecan's reasonable
pricing structure, but the p-System and UCSD Pascal gradually lost the market to native operating systems and compilers.