Zeidman Consulting Concludes that Microsoft Did Not Copy CP/M from Digital Research to Create MS-DOS

Software forensics pioneer Bob Zeidman resolved the long-standing controversy and is offering a cash reward to anyone who can prove him wrong

CUPERTINO, Calif.—August 8, 2016—Zeidman Consulting, a leading provider of consulting and expert witness services for intellectual property litigation, today announced that, after a comprehensive source code comparison, its president Bob Zeidman found no evidence that copied from Digital Research to create MS-.

For decades there have been rumors that in 1980, when IBM chose MS-DOS over CP/M for its PC operating system, Microsoft had copied CP/M and that the credit, and the money, should have gone to Digital Research, Inc. (DRI) and its CEO, Gary Kildall. Recently, Microsoft donated the previously unavailable source code for MS-DOS to the Computer History Museum in Mountain View, California, and a more complete version of the CP/M source code was discovered. Renowned forensic scientist Bob Zeidman compared the two programs using the same methodology that he uses as an expert witness in high-profile legal cases such as Oracle v. Google and ConnectU v. Facebook. He found no evidence that Microsoft copied CP/M source code to create MS-DOS. Zeidman presented his findings on Saturday, August 6, at the Vintage Computer Festival at the Computer History Museum. His presentation and the full results of his analysis are available here.

After years of research, Zeidman developed the algorithms for multidimensional correlation that determine which sections of code are similar for multiple different reasons. After that determination, an expert can use an iterative filtering process that Zeidman developed to decide whether the correlation is due to any one of the six reasons for correlation: third-party code, code generation tools, commonly used names, common algorithms, common programmers, or copying. The correlation algorithms are implemented in the forensic software tool CodeSuite®, developed by Zeidman and sold by his software company Software Analysis and Forensic Engineering.

“Based on my comprehensive comparison of Microsoft’s MS-DOS and Digital Research’s CP/M source code, I’m confident in my assessment that Microsoft did not copy CP/M code from Digital Research to create MS-DOS,” said Zeidman. “This question has finally been laid to rest.”

Zeidman also found no evidence to support a related rumor that there is a secret command in MS-DOS that can be called to print Gary Kildall’s name and a copyright notice for DRI.

Zeidman is standing behind his analysis and conclusion. He will offer a $100,000 reward to anyone who can use accepted forensic techniques to prove that Microsoft copied MS-DOS from DRI’s CP/M. He will offer another $100,000 reward to anyone who can find a secret function in MS-DOS that prints Gary Kildall’s name or a copyright notice for DRI. The award details and specific criteria will be announced shortly.

About Bob Zeidman

Bob Zeidman is considered a pioneer in the fields of analyzing and synthesizing software source code. He is the president and founder of Zeidman Consulting, a premier contract research and development firm in Silicon Valley that provides engineering consulting to law firms regarding intellectual property disputes, and he is the president and founder of Software Analysis and Forensic Engineering Corporation, the leading provider of software intellectual property analysis tools, having pioneered the field. His book The Software IP Detective’s Handbook is one of the main books for engineers and lawyers on software intellectual property.

Media Contact

Todd Lane

Antenna Group



Topics covered in this article