Microsoft Open-Sources the Original MS-DOS on GitHub
In September 2018, Microsoft re-released MS-DOS 1.25 and 2.11's source code on GitHub under the MIT license — a genuinely open release, four years after a 2014 version that was source-available but not truly open.
In September 2018, Microsoft published the original source code for MS-DOS 1.25 and MS-DOS 2.11 on GitHub, under the MIT license — a genuinely permissive open-source release, distinct from an earlier, more limited disclosure four years prior.
The 2014 release wasn’t really open source
Microsoft had already made MS-DOS 1.25 and 2.0’s source available in March 2014, through the Computer History Museum — but under terms that amounted to “look but don’t touch,” without a genuine open-source license permitting reuse, modification, or redistribution. The 2018 GitHub release corrected this specifically: the same source (updated to reference 2.11 rather than 2.0), this time under the MIT license, a real, standard, permissive open-source license.
What the repository actually contains
The GitHub repository (microsoft/MS-DOS) includes the original source code and compiled binaries for MS-DOS 1.25 and 2.0, plus the source code for MS-DOS 4.00 — a version jointly developed by IBM and Microsoft. Publishing it on GitHub specifically, rather than as a downloadable archive from a museum’s website, made the historical source dramatically easier to browse, search, and reference than the 2014 release had been.
Why this news matters directly to FreeDOS
FreeDOS exists as an independently-written, from-scratch reimplementation of DOS functionality — it was never built from Microsoft’s actual MS-DOS source, which remained proprietary and inaccessible throughout FreeDOS’s early development. Microsoft’s 2018 release doesn’t change FreeDOS’s own codebase, but it gives researchers, historians, and developers a genuine, legally clear reference for exactly how the original MS-DOS worked internally — valuable historical and technical context for the same DOS-compatibility space FreeDOS occupies, even without directly touching FreeDOS’s own code.
Why the licensing distinction mattered so much
The difference between “source visible for reference” (2014) and “source under a real open-source license” (2018) is significant — an MIT-licensed release permits genuine reuse, study, and modification without the legal ambiguity of the earlier disclosure. Microsoft choosing to correct this four years later, doing it properly the second time, reflects a broader, gradual shift in how the company approached open-sourcing pieces of its own historical software during this period.
Sources: GitHub - microsoft/MS-DOS, Re-Open-Sourcing MS-DOS 1.25 and 2.0 — Windows Command Line Blog