In a previous paper , I compared DOS
from Microsoft and CP/M from Digital Research Inc. (DRI) to determine whether
the original DOS source code had been copied from CP/M source code as had been
rumored for many years  . At the time, the source code for CP/M was
publicly available but the source code for DOS was not. My comparison was
limited to the comparison of the DOS 1.11 binary code and the source code for
CP/M 2.0 from 1981. Since that time, the Computer History Museum in Mountain
View, California received the source code for DOS 2.0 from Microsoft and was
given permission to make it public. The museum also received the source code
for DOS 1.1 from Tim Paterson, the developer who was originally contracted by
Microsoft to write DOS. In this paper, I perform a further analysis using the
newly accessible source code and determine that no code was copied. I further
conclude that the commands were not copied but that a substantial number of the
system calls were copied.
Zeidman, B. (2014) A Code Correlation Comparison of the DOS and CP/M Operating Systems. Journal of Software Engineering and Applications, 7, 513-529.