UCSD p-System

The UCSD p-System or UCSD Pascal System was a portable highly machine independent operating system developed in 1978 by the Institute for Information Systems of the University of California, San Diego to provide all students with a common operating system that could run on any of the then available microcomputers as well as campus PDP-11 minicomputers.

The machine independence was achieved by defining a virtual machine called the p-Machine (or pseudo-machine, which many users began to call the "Pascal-machine" like the OS, although the UCSD documentation always used "pseudo-machine") with its own instruction set called p-Code (or pseudo-code). This p-Code was optimized specifically for generation by the Pascal programming language and all the original development was done in UCSD Pascal. Each hardware platform then only needed a p-Code interpreter program written for it to port the entire p-System and all the tools to run on it.

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.

• 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.

• Version III

Custom version written for Western Digital to run on their Pascal Micro-Engine microcomputer.

• Version IV

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.

References

• UCSD PASCAL System II.0 User's Manual March 1979 - Institute for Information Systems, UCSD. Copyright 1978 Regents of the University of California, San Diego.