UCSD p-SystemThe 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
- Version II
- Version III
- Version IV