Microsoft and IBM join forces to Open Source MS-DOS 4.0

Microsoft and IBM Open Source their infamous MS-DOS 4.0 OS

Ten years ago, Microsoft Open Sourced their MS-DOS 1.25 and MS-DOS 2.0 operating systems, and today they have expanded their open source legacy OS offerings with MS-DOS 4.0. Now, the source code for DOS 4.0 is now available on GitHub.

This open source release is for “historical reference and will be kept static”. In other words, Microsoft will not be accepting pull requests. Even so, there is nothing stopping people from forking the OS to create something new and different. After all, the OS is now available under an MIT license.

By making this legacy OS Open Source, Microsoft has preserved their OS online for future users to enjoy. This Open Source release came thanks to Connor “Starfrost” Hyde. He uncovered beta binaries of DOS 4.0 within the software collection of former Microsoft Chief Technical Officer Ray Ozzie. This find is what promted Microsoft and IBM to Open Source DOS 4.0. More information about the “Ozzie Drop” is available here.

With this Open Source release, PC users can now utilise this old OS on classic PC hardware and even classic PC emulators. Microsoft’s Scott Hanselman and Jeff Wilcox have confirmed that they have ran the OS successfully on an IBM PC XT, “a newer Pentium”, and using the open source PCem and 86box emulators.

Hopefully Microsoft will continue to open source their classic PC operating systems. It would be nice to see MS-DOS 3.0 become Open Sourced, or perhaps some of Microsoft’s early Windows OS’.

You can join the discussion on Microsoft Open Sourcing MS-DOS 4.0 on the OC3D Forums.