Believe it or not, not everything is based on C. There are current, shipping, commercial OSes written before C was invented, and now others in both newer and older languages that don’t involve C at any level or layer.
Computer hardware is technology yet very few people can design their own processor, or build a graphics card. But software is a form of culture. Open source is created by volunteers, even if they end up getting paid jobs doing it. Even rejecting open source is a choice: paying for Windows or macOS instead reflects a preference.
This is especially visible when it comes to text editors, and even more so about programming languages. People get passionate about this stuff. So statements such as “C isn’t a programming language any more” can be upsetting. Most people live and work in the cultures that are Unix and Windows and if they are all you’ve ever known, or know best, then it’s easy to think they are the whole world.
But that doesn’t make it true.
The roots of C
C fans tend to regard BCPL as an unimportant transitional step, but it was used in two celebrated OSes. One was the TRIPOS operating system, later used as the original basis of AmigaOS. The core system software of the original GUI workstation, the Xerox Alto, was also written in BCPL, although much of it was later rewritten in Mesa. The Alto OS survived into the late 1990s as GlobalView, which Xerox sold as a high-end desktop publishing tool.
Algol and Burroughs
In the 1960s, ALGOL was huge. It’s the granddaddy of most modern imperative languages.
Burroughs Corporation designed a series of mainframes, the Burroughs Large Systems, around the pioneering idea of writing the OS and all applications in a high-level language, ALGOL. The first machine, the B5000, was launched in 1961. Burroughs merged with Sperry UNIVAC in 1986 to form Unisys. The Unisys Clearpath MCP OS is a direct descendant of the B5000’s MCP or Master Control Program. (Yes, the same name as the big baddie in Tron.)
MCP was the first commercial OS to support virtual memory and shared libraries. Its purely stack-based design inspired Chuck Moore to develop Forth, HP to design the HP3000 mid-range computers, and influenced Alan Kay in the development of Smalltalk at Xerox PARC.
The current version of ClearPath MCP is 20.0, released in May 2021.
Wirth a go
Swiss boffin Niklaus Wirth worked at Xerox PARC for two one-year sabbaticals. Today he’s best known for inventing Pascal, which happened to catch on as an applications language – notably as Borland’s Delphi. An earlier implementation, the UCSD p-System, was a complete OS – one of the three IBM offered for the original PC in 1981.
Pascal was just one stage in a series of “Wirthian” languages. The successor to Pascal was Modula, but it was quickly superseded by Modula-2, based on Wirth’s time working with Mesa on the Alto at Xerox PARC. Modula-2 was specifically designed for OSes as well as apps.
After his first sabbatical in Palo Alto in 1976-1977, once Wirth got back home to ETH Zürich in 1977, he and his team designed and built the Lilith workstation as a cheaper replacement for the $32,000 Alto. Its object-oriented OS, Medos-2, was entirely built in Modula-2.
Meanwhile, in the USSR, a team at the Soviet Academy of Sciences in Novosibirsk, inspired by Wirth’s work but limited by COCOM import restrictions, built their own OS called Excelsior in Modula-2, which ran on a series of workstations called Kronos.
Wirth returned to Xerox PARC in 1984-1985, and after that trip, back at ETH he designed the Ceres workstation, with an OS implemented in a new language, Oberon, whose text-based tiling-window interface inspired the successor to Unix, Plan 9 from Bell Labs.
(The influence went both ways. A team at Xerox PARC developed Pascal into the Euclid language, and a variant was e
