The article notably omits Multics, which was written in PL/I: https://en.wikipedia.org/wiki/Multics https://en.wikipedia.org/wiki/Multics Multics, first releas

The article notably omits Multics, which was written in PL/I: https://en.wikipedia.org/wiki/Multics https://en.wikipedia.org/wiki/Multics Multics, first released in 1969, was a major influence on Unix. From the Wikipedia article: > Multics was the first operating system to provide a hierarchical file system, and file names could be of almost arbitrary length and syntax. A given file or directory could have multiple names (typically a long and short form), and symbolic links between directories were also supported. ... It was also the first to have a command processor implemented as ordinary user code – an idea later used in the Unix shell. It was also one of the first written in a high-level language (Multics PL/I), after the Burroughs MCP system written in ALGOL.