 Unix was one of the first operating system kernels implemented in a language other than assembly.Earlier instances include the Multics system (which was written in PL/I) and Master Control Program (MCP) for the Burroughs B5000 (which was written in ALGOL) in 1961.In around 1977, Ritchie and Stephen C. Johnson made further changes to the language to facilitate portability of the Unix operating system.