Editing UCSD Pascal (section)

==Versions==
[[File:UCSD2.png|thumb|Filer, the [[file manager]]]]
There were four versions of UCSD p-code engine, each with several revisions of the p-System and UCSD Pascal. A revision of the p-code engine (i.e., the p-Machine) meant a change to the p-code language, and therefore compiled code is not portable between different p-Machine versions. Each revision was represented with a leading Roman Numeral, while operating system revisions were enumerated as the "dot" number following the p-code Roman Numeral. For example, II.3 represented the third revision of the p-System running on the second revision of the p-Machine.

===Version I===
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.

===Version II===
Widely distributed, available on many early microcomputers. Numerous versions included [[Apple II]] ultimately [[Apple Pascal]], DEC PDP-11, [[Intel 8080]], [[Zilog Z80]], and [[MOS 6502]] based machines, Motorola 68000 and the [[IBM PC]] (Version II on the PC was restricted to one 64K [[code segment]] and one 64K stack/heap [[data segment]]; Version IV removed the code segment limit but cost a lot more{{quantify|date=October 2010}}).

Project members from this era include Dr Kenneth L Bowles, [[Mark Allen (software developer)|Mark Allen]], Richard Gleaves, Richard Kaufmann, Pete Lawrence, [[Joel McCormack]], Mark Overgaard, Keith Shillington, Roger Sumner, and John Van Zandt.

===Version III===
Custom version written for [[Western Digital]] to run on their Pascal MicroEngine microcomputer. Included support for parallel processes for the first time.

===Version IV===
Commercial version, developed and sold by SofTech. Based on Version II; did not include changes from Version III. Did not sell well due to combination of their pricing structure, performance problems due to p-code interpreter, and competition with native operating systems (on top of which it often ran). After SofTech dropped 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. Available for the [[TI-99/4A]] equipped with p-code card, [[Commodore PET|Commodore CBM 8096]], Sage IV, [[HP_9000#Series_200|HP 9000]], and [[BBC Micro]] with 6502 second processor.<ref name="beebug198501_pascal">{{ cite magazine | url=https://archive.org/details/beebugv0308/page/7/mode/1up | title=Acornsoft's UCSD Pascal System | magazine=Beebug | last1=Maher | first1=John | date=January 1985 | access-date=2 July 2024 | pages=7–10 }}</ref>