The most widely known version is occam 2; its programming manual was written by Steven Ericsson-Zenith and others at Inmos.

However, the program will neither spin nor poll; thus terms like wait, hang or yield may also convey the behaviour; also in the context that it will not block other independent processes from running.)

Examples (c is a variable): SEQ introduces a list of expressions that are evaluated sequentially.

occam 1[2] (released 1983) was a preliminary version of the language which borrowed from David May's work on EPL and Tony Hoare's CSP.

occam 2[3] is an extension produced by Inmos Ltd in 1987 that adds floating-point support, functions, multi-dimensional arrays and more data types such as varying sizes of integers (INT16, INT32) and bytes.

A revised Reference Manual describing occam 3 was distributed for community comment,[5] but the language was never fully implemented in a compiler.