The parentage of the MS-DOS operating system is to be decided in court. Tim Paterson, who sold the Intel-compatible operating system 86-DOS (aka QDOS) to Microsoft in 1980 is suing author and former Times editor Harold Evans, and his publisher Time Warner, for defamation. Paterson’s work became Microsoft’s first operating system – it subsequently rebadged QDOS as MS-DOS version 1.0, and it was made available with the original IBM PC.

In his book They Made America published last year, Evans devoted a chapter to the late, great Gary Kildall, founder of Digital Research. Evans described Paterson’s software as a “rip-off” and “a slapdash clone” of Kildall’s CP/M, then the leading operating system for micro computers.

Paterson’s Seattle Computer Products (SCP) made an 8086 plug-in card for the S-100 computer, and Paterson wrote an operating system to go with the board. His suit admits that he wanted the API for his operating system to be compatible with the market leader CP/M.

“Plaintiff felt that the format used by CP/M was a significant bottleneck so he turned to the Microsoft Stand-Alone Disk BASIC and used a File Allocation Table,” the suit says. The resulting board and OS shipped in August 1980.

Paterson claims that Evans falsely accused Kildall of being the “inventor” of DOS, and for citing former Intel engineer, now Stanford lecturer John Wharton for pointing out that Paterson used Kildalls INT-21 mechanism “almost unaltered”.

Paterson has endured “great pain and mental anguish” and is seeking “over $75,000” in damages, plus costs.

Is it wise? The case, should it come to court, will hinge on a technical evaluation of QDOS, and central to case is one document in particular. It’s Paterson’s original “Programer’s Manual” (sic) for his operating system, illustrated here.

Several weeks ago, Wharton told The Register that he hadn’t been contacted by Evans or his researchers, and that the quotes used in the book were several years old.

Evans says he’ll “vigorously contest” the defamation claims.