Mark Williams Company

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Mark Williams Company logo.

The Mark Williams Company was a small software company in Chicago, Illinois (later moved to Northbrook, Illinois) that created Coherent, one of the first Unix-like operating systems for IBM PCs and several C programming language compilers. It was founded by Robert Swartz in 1977[1] and discontinued operations in 1995. The name comes from the middle name of Robert Swartz's father, William Mark Swartz.

Robert Swartz moved the company (originally producing a soft drink called Dr. Enuf[2][3]) into software with his father's help and the company became known as the Mark Williams Company.

Mark Williams won a patent lawsuit centered on 'byte ordering'.[citation needed] Separately and at that time,[when?] Linux had made serious inroads in the UNIX clone market. Since Coherent was a commercially available package and Linux was distributed freely on the Internet via their GNU public license, Coherent sales plummeted and Swartz had no choice but to cease operations in 1995.


  • Produced Coherent, a clone of Unix.
  • csd, C source debugger.[4]
  • Let's C, low-cost professional C compiler for the IBM PC.[citation needed]
  • Mark Williams C for CP/M-86.
  • Mark Williams C for the Atari ST, first major C programming environment for the ST computers.
  • XYBasic, a process control BASIC running on CP/M that could be burned on to memory (EPROM) and run on an 8080 standalone processor.


  1. ^ Ness, Stephen. "XYBASIC". Ness Software. Retrieved 20 May 2017.
  2. ^ Lee, Joseph. "Dr. Enuf: The story of Johnson City Tennessee's most famous product". Retrieved 2013-03-03. In 1949 William Mark Swartz, President of Mark Williams Chemical Co. of Chicago, Ill., decided to create a soft drink that would relieve fatigue, headaches, indigestion etc….  He applied for a trademark for the drink on May 19, 1951.
  3. ^ Sauceman, Fred (2009). The Place Setting: Timeless Tastes of the Mountain South. 3. Mercer Univ. Press. pp. 89–97. ISBN 9780881461404. According to corporate lore, Bill Schwartz [sic], a Chicago chemist, developed the formula after hearing his co-workers complain of lethargy.
  4. ^ "Does your C compiler understand you're only human? (advertisement)". PC Magazine. May 14, 1985. p. 284.

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