History
In 1961, the MCP was the first OS written exclusively in a high-level language (HLL). The Burroughs Large System (B5000 and successors) were unique in that they were designed with the expectation that all software, including system software, would be written in an HLL rather than in assembly language, which was a unique and innovative approach in 1961.
Unlike IBM, which faced hardware competition after the departure of Gene Amdahl, Burroughs software was designed only to run on proprietary hardware. For this reason, Burroughs was free to distribute the source code of all software it sold, including the MCP, which was designed with this openness in mind. For example, upgrading required the user to recompile the system software and apply any needed local patches. At the time, this was common practice, and was necessary as it was not unusual for customers (especially large ones, such as the Federal Reserve) to modify the program to fit their specific needs. As a result, a Burroughs Users Group was formed, which held annual meetings and allowed users to exchange their own extensions to the OS and other parts of the system software suite. Many such extensions have found their way into the base OS code over the years, and are now available to all customers. As such, the MCP could be considered one of the earliest open-source projects.
Burroughs was not the first manufacturer to distribute source code and indeed was a late entry to electronic computing (compared to its traditional rivals NCR, IBM, and Univac) but the situation outlined in the previous paragraph presages the current computing culture where OSS dominates. Ironically, now that MCP runs on commodity hardware some elements of the MCP based software suite are no longer made available in source form by Unisys.
The MCP was the first commercial OS to provide virtual memory, which has been supported by the Burroughs large systems architecture since its inception. This scheme is unique in the industry, as it stores and retrieves compiler-defined objects rather than fixed-size memory pages, as a consequence of its overall non-von Neumann and uniformly stack based architecture.
Read more about this topic: Burroughs MCP
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