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In page P-code machine:

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In the early 1980s, at least two operating systems achieved machine independence through extensive use of P-code[citation needed]. The Business Operating System (BOS) was a cross-platform operating system designed to run P-code programs exclusively. The UCSD p-System, developed at The University of California, San Diego, was a self-compiling and self-hosting operating system based on P-code optimized for generation by the Pascal language.