Toggle Menu

Zeidman Consulting Concludes that Microsoft Did Not Copy CP/M Code but Did Copy System Calls 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 Microsoft copied CP/M from Digital Research to create MS-DOS but did find evidence that system calls were copied.

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 intellectual property 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.

"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."

However, Zeidman did confirm that the CP/M system calls were copied. System calls are used by a computer application program to request a service from the operating system, such as outputting text to a console or a printer, determining the amount of memory that is installed in the system, or reading from and writing to a hard disk. The code to implement the system calls was not copied, but at least 22 of the system calls in both systems have the same function and the same function number.

"While I'm not a lawyer, my experience in over 175 intellectual property cases tells me that DRI might have had a copyright claim for the system calls that it could have litigated against Microsoft. On the other hand, there is a good chance Microsoft could have beaten such litigation by claiming it was a 'fair use' of the system calls," said Zeidman.

Zeidman 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 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.

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 source code from DRI's CP/M source code. He will offer another $100,000 reward to anyone who can demonstrate or find source code for 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.

After years of research, Zeidman developed the algorithms for multidimensional software 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.

About Zeidman Consulting
Zeidman Consulting, headquartered in Silicon Valley, is one of the leading firms for analyzing and reverse-engineering software and providing expert witness services for IP litigation. Zeidman Consulting has been involved in some of the largest and landmark high tech IP cases in history.

Bob Zeidman Earns IEEE Outstanding Engineer Award for Pioneering Contributions to Software Forensics.
10981 Willow Valley Ct
Las Vegas, NV 89135
Tel +1 (650) 741-5809
S.A.F.E. Corporation
Visit our sister site Software Analysis and Forensic Engineering Corporation, the leading provider of software analysis and comparison tools for IP litigation.SAFE Corporation