 | This article'slead sectionmay be too short to adequatelysummarize the key points. Please consider expanding the lead toprovide an accessible overview of all important aspects of the article.(February 2023) |
| Coherent | |
|---|---|
 | |
 Coherent 4.2.10 installer | |
| Developer | Mark Williams Company |
| OS family | Unix-like |
| Working state | Discontinued |
| Source model | Closed source;open sourced in 2015 |
| Initial release | 1980; 45 years ago (1980) |
| Latest release | 4.2.14 / 1994; 31 years ago (1994) |
| Available in | English |
| Supported platforms | PDP-11,x86 (8088,286,386,486),Motorola 68000,Zilog Z8000 |
| Kernel type | Monolithic |
| Default user interface | Command-line (KornShell) |
| License | 2015:BSD-3-Clause[1] Original: Proprietary |
Coherent is a clone of theUnixoperating system forIBM PC compatibles and othermicrocomputers, developed and sold by the now-defunctMark Williams Company (MWC). Historically, the operating system was a proprietary product, but it becameopen source in 2015, released under theBSD-3-Clause license.[1]
Coherent was not Unix; the Mark Williams Company had no rights to either the Unixtrademark or theAT&T/Bell Labssource 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 includedDennis 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." However, he also stated that:[2]
[...] 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 theUniversity 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 (fromAuckland,New Zealand), the later author ofGhost.[3]
Coherent was originally written for thePDP-11 range of minicomputers in 1980,[4] then ported to various early 1980smicrocomputer systems includingIBM PC compatibles and machines based on theZilog Z8000 andMotorola 68000. Initially sold toOEMs, starting 1983 it was available on the consumer market from MWC directly. At this point, Coherent 2.3 offered roughly the functionality ofVersion 7 Unix on PC hardware, including thenroff formatter but not theBSD extensions offered by competing Unix/clone vendors; compared to its competitors, it was a small system distributed on only sevendouble-sidedfloppy disks, costing onlyUS$500 for a license.[5][4]
Coherent runs on mostIntel-based PCs withIntel 8088,286,386, and486processors. Coherent version 3 for Intel-based PCs requires at least a 286; Coherent version 4 for Intel-based PCs requires at least a 386. Like a true Unix, Coherent is able tomultitask and supportmultiple users. From version 4, released 1992,[6] Coherent also has support forX11 andMGRwindowing systems.[7][8]
Later versions of Coherent (version 4 and higher) support features common in modern Unix-like systems, including a version ofMicroEMACS, access toFAT16file systems,[citation needed] anoptimizing[citation needed]Ccompiler, and a modified version of TaylorUUCP.[citation needed] The final releases of Coherent also fully support theiBCSCOFF binary standard,[citation needed] which allow binary compatibility withSCO Unix applications, includingWordPerfect,Lotus 1-2-3, and severalMicrosoft applications includingQuickBASIC,Microsoft Word, andMultiPlan. The last 386 versions supportedvirtual memory, but notdemand paging.
AZilog Z8000 port of Coherent was also used by the canceledCommodore 900 system.[9]
In 1983, NCSC (a subsidiary ofNixdorf) announced a port of Coherent to IBM mainframes, in the form of a Unix compatibility subsystem for IBM'sDOS/VS andDOS/VSE and Nixdorf'sEdos/VS andEdos/VSE operating systems, known as Programmer Work Station/VSE-Advanced Functions, or PWS/VSE-AF for short.[10]
The Mark Williams Company closed in 1995.[11]
On January 3, 2015, Coherent sources were released under theBSD-3-Clause license.[1]
BYTE in 1984 called Coherent a "highly compatible UNIX Version 7 lookalike".[12] In 1985 it criticized the difficulty of installation, but stated that "as a UNIX clone, Coherent is amazingly complete ... it should be easy to port programs ... the price of $495 is a bargain".[13]
Coherent "is not without drawbacks",UnixWorld in 1985 said, but favorably cited its low hardware requirement, "only $500" cost, and clear documentation. The magazine found that Coherent was "surprisingly complete for a rewrite", with good interactive and multiuser performance, and estimated that up to eight tasks could be run while remaining usable. While noting the inability to run theAIM Multiuser Benchmark, and lack of certain utilities such ascsh andSCCS,UnixWorld concluded that "Coherent is still a good choice for the IBM PC/XT owner who wants a Unix-compatible operating system at a very reasonable cost and low system hardware overhead".[4]
Early 1990s reviews of Coherent pointed out that the system was much smaller than other contemporary Unix offerings, as well as less expensive at US$99.95, but lacking in functionality[14] and software support.[15]PC Magazine called Coherent 3.0 a "time capsule" that captured the state of Unix in the late 1970s, without support formice,LANs orSCSI disks, good for learning basic Unix programming but not for business automation.[14] A review in theAUUG's newsletter was more positive, favorably comparing Coherent toMKS Toolkit,Minix andXenix, and suggesting it might fill a niche as a low-end training platform.[16]
