86-DOS - Intellectual Property Dispute

Intellectual Property Dispute

When Digital Research founder Gary Kildall examined PC DOS and found that it duplicated CP/M's programming interface, he wanted to sue IBM, which at the time claimed that PC DOS was its own product. However, Digital Research's attorney did not believe that the relevant law was clear enough to sue. Nonetheless, Kildall confronted IBM and persuaded them to offer CP/M-86 with the PC in exchange for a release of liability.

Controversy has continued to surround the similarity between the two systems. Perhaps the most sensational claim comes from Jerry Pournelle, who claims that Kildall personally demonstrated to him that DOS contained CP/M code by entering a command in DOS that displayed Kildall's name; as of 2006 Pournelle has not revealed the command and nobody has come forward to corroborate his story. A 2004 book about Kildall says that he used such an encrypted message to demonstrate that other manufacturers had copied CP/M, but does not say that he found the message in DOS; instead Kildall's memoir (a source for the book) pointed to the well-known interface similarity. Paterson insists that the 86-DOS software was his original work, and has denied referring to or otherwise using CP/M code while writing it. After the 2004 book appeared, he sued the authors and publishers for defamation. The court ruled in summary judgement that no defamation had occurred, as the book's claims were opinions based on research or were not provably false.