Coherent (operating system)
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Coherent 4.2.10 installer
|Company / developer||Mark Williams Company|
|Source model||Closed source|
|Latest release||4.2.10 / 1994|
|Supported platforms||PDP-11, 8088, 286, 386, 486, Zilog Z8000|
The Coherent operating system was a Version 7 Unix clone by the now-defunct Mark Williams Company, originally produced for the PDP-11 in 1980. A port was introduced in 1983 as the first Unix-like system for IBM PC compatible computers.
Coherent was able to run on most Intel-based PCs with Intel 8088, 286, 386, and 486 processors. Coherent version 3 for Intel-based PCs required at least a 286, Coherent version 4 for Intel-based PCs required at least a 386. Like a true Unix, Coherent was able to multitask and support multiple users. From version 4 on Coherent also had support for X11 and MGR windowing systems.
Later versions of Coherent (version 4 and higher) supported features common in modern Unix-like systems, including a version of MicroEMACS, access to DOS FAT16 File systems, an optimizing C compiler with linker, and a modified version of Taylor UUCP. The final releases of Coherent also fully supported the iBCS COFF binary standard, which allowed binary compatibily with SCO Unix applications, including WordPerfect, Lotus 1-2-3, and several Microsoft applications including QuickBASIC, Microsoft Word, and MultiPlan. There was no support for virtual memory or demand paging. Coherent predates both MINIX and Linux by many years.
Coherent was not Unix; the Mark Williams Company had no rights to either the Unix trademark or the AT&T/Bell Labs source code. In the early years of its existence, MWC received a visit from an AT&T delegation looking to determine whether MWC was infringing on AT&T Unix property. The delegation included Dennis Ritchie, who concluded that "it was very hard to believe that Coherent and its basic applications were not created without considerable study of the OS code and details of its applications" and "that looking at various corners [for peculiarities, bugs, etc. that I knew about in the Unix distributions of the time] I couldn't find anything that was copied. It might have been that some parts were written with [AT&T] source nearby, but at least the effort had been made to rewrite. If it came to it, I could never honestly testify [...] that what they generated was irreproducible from the manual."
Much of the operating system was written by alumni from the University of Waterloo: Tom Duff, Dave Conroy, Randall Howard, Johann George, and Trevor John Thompson. Significant contributions were also made by people such as Nigel Bree (from Auckland, New Zealand). Nigel went on to write "Ghost" - later bought out and fully commercialized as Norton Ghost.
The Mark Williams Company closed in 1995.
Some websites offer Coherent for download, although the copyright status of it nowadays is unclear but for Hans Bezemer's site. While Coherent does not have the features of a modern Unix-like OS such as Linux, it is still a viable solution for those looking to run Unix on a very old computer such as a 286-based machine.
Sources are available for version 4.2.14. However, they don't work. Sources for the latest available version are also available, but under NDA.
- Dean Hannotte (12 June 1984). A Good Buy on UNIX. The Mark Williams Company's COHERENT operating systems is a rewritten version of the seventh edition of UNIX, with some extensions and enhancements. Regrettably, it has incoherencies.. PC Magazine. pp. 250–254. ISSN 08888507.
- Andrzej Popielewicz's GNU stuff for Coherent website
- FTP archive for Coherent
- Coherent history archive
- Installation Media for Coherent 4.2.10
- Coherent Manual (27 MB)