Microsoft made available under open source license MIT the source codebinaries, images and documentation of MS-DOS 4.0. The welcome news was communicated by Scott Hanselman, VP Developer Community and Jeff Wilcox, Head of Open Source Programs Office, in a post.
“10 years ago, Microsoft released the MS-DOS 1.25 and 2.0 source code for the Computer History Museum. […] Today, in collaboration with IBM and in the spirit of open innovation, we are releasing the source code for MS-DOS 4.00 under the MIT license“, the post begins.
Hanselman and Wilcox recall the “rather complex and fascinating” story behind version 4.0 of DOS, with Microsoft collaborating with IBM on parts of the code, but creating “a branch of DOS called Multitasking DOS that did not see wide release”. Multitasking DOS, or MT-DOS, was later abandoned by Microsoft to focus on MS-DOS 5.x and MS-DOS 6.x before the Windows era.
Microsoft decided to open source MS-DOS 4 after that a young English researcher (Connor “Starfrost” Hyde) has come into contact with Ray Ozzie. The former technical director had in his archives some unreleased beta binaries of MS-DOS 4.0, which he had received while working at Lotus. Starfrost was interested in documenting the relationship between DOS 4, MT-DOS, and OS/2 and was also trying to convince the Microsoft Open Source Programs Office (OSPO) to release the DOS 4 code.
Working with Internet archivists and software enthusiasts, OSPO and Starfrost managed to find the complete source code of MS-DOS 4.00which Microsoft has decided to release alongside the Ozzie beta binaries, PDF files of the original documentation, and the Image files that can be used with PC emulators (PCem, 86Box) to bring the operating system back to life on modern PCs.
Microsoft says that the images have been successfully tested directly on an original IBM PC XT PC, a more recent Intel Pentium CPU-based system and within the aforementioned open source PC emulators.
