On Tuesday, Microsoft donated the source code of MS DOS 1.1 and 2 to the Computer History Museum (CHM), along with the first version of Word for Windows.

CHM chairman, Len Shustek, said: "Version 1.1 fits an entire operating system – limited as it was – into only 12KB of memory, which is tiny compared to today's software. We think preserving historic source code like these two programs is key to understanding how software has evolved from primitive roots to become a crucial part of our civilization."

The code can be downloaded here for MS DOS and here for Word for Windows, but not distributed further under the terms of the license.

Roy Levin, engineer and managing director for Microsoft Research, said: "MS-DOS and Word for Windows built the foundation for Microsoft's success in the technology industry. "By contributing these source codes to the Computer History Museum archives, Microsoft is making these historic systems from the early era of personal computing available to the community for historical and technical scholarship."