What is Language Environment?

Among OpenVMS's notable features is the Common Language Environment, a strictly defined standard that specifies calling convention for functions and routines, including use of stacks, registers, etc., independently of programming language. Because of this, it is possible to call a routine written in one language (e.g. FORTRAN) from another (e.g COBOL), without needing to know the implementation details of the target language. OpenVMS itself is implemented in a variety of different languages (primarily BLISS, VAX Macro and C), and the common language environment and calling standard supports freely mixing these languages, as well as Ada, PL/I, Fortran, Basic, and others. This is in contrast to a system such as Unix, which is implemented nearly entirely in the C language.