A Good Buy on UNIX Special Report by Dean Hannotte from the June 12, 1984 issue of PC Magazine The Mark Williams Company’s COHERENT operating system is a rewritten version of the seventh edition of UNIX, with some extensions and enhancements. Regrettably, it has incoherencies. The Mark Williams Company’s COHERENT operating system is a State-of-the-art microcomputer implementation of AT&T’s UNIX, without the state-of-the-art AT&T licensing fees. It is a completely rewritten version of the seventh edition of UNIX and includes some of its multi-user and multitasking abilities.