Coherent (operating system)
The 
Coherent operating system was introduced in 
1983 by the now-defunct Mark Williams Company as one of the first 
Unix-like computer operating systems for IBM PC-compatible 
computers. Coherent was capable of running on most Intel-based PCs with 
286, 
386, and 
486 processors and, like a true 
Unix, was capable of 
multitasking and of having multiple users. Coherent also had support for 
X11.
Coherent is sometimes mistakenly referred to as "Coherent Unix", which is incorrect. Coherent was based on the specifications of Unix Version 7, without reference to any of the Unix source code, either from Bell Labs or BSD.
The Mark Williams Company went bankrupt in 1995.
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