Microsoft has made available under the MIT open source license the source code, binaries, images, and documentation of MS-DOS 4.0. This exciting 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 source code of MS-DOS 1.25 and 2.0 to 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,» begins the post.
Hanselman and Wilcox recall the «rather complex and fascinating» history behind the DOS 4.0 version, with Microsoft collaborating with IBM for parts of the code, creating however «a branch of DOS called Multitasking DOS that did not see widespread 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 has decided to make MS-DOS 4 open source after a young English researcher (Connor «Starfrost» Hyde) contacted Ray Ozzie. The former chief technical officer had in his archives some unpublished beta binaries of MS-DOS 4.0, which he had received while working at Lotus.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 4.00, which Microsoft has decided to release along with Ozzie’s beta binaries, PDF files of the original documentation, and image files that can be used with PC emulators (PCem, 86Box) to bring back the operating system to modern PCs.
Microsoft states that the images have been successfully tested directly on an original IBM PC XT, a more recent system based on an Intel Pentium CPU, and within the aforementioned open-source PC emulators.
