After versions 1.25 and 2.0, the Source code of MS-DOS v4.0 has just been published online under the MIT license by Microsoft, in collaboration with IBM. And it’s not just any version of MS-DOS 4. Explanations.
In March 2014, Microsoft delivered the Source code for two operating systems, MS-DOS 1.25 and 2.0, to the Computer History Museum and then released them for reference on Github. This same account will now host a particular version of MS-DOS 4.00 under MIT license.
This discovery was made by an English researcher, Connor “Starfrost” Hyden, a software collector. Among the floppy disks he owned were unreleased beta binaries of DOS 4.0, sent to him while he was still working at Lotus.
What’s quite fascinating is the winding history of versions 4.0 of DOS: Microsoft actually partnered with IBM for parts of the code, but also created a branch of DOS called Multitasking DOSwhich was not widely distributed.
Incidentally, Starfrost chose to contact Microsoft’s OSPO to explore the possibility of releasing the Source for DOS 4, as it was working on documenting the relationship between DOS 4, MT-DOS, and what would ultimately become OS/ 2. “ Some later versions of these Multitasking DOS binaries can be found on the internet, but these new beta binaries appear to be much older, unreleased, and also include the Source ibmbio.com », Explains Jeff Wilcox, head of the Open Source Programs Office, on the publisher’s blog.
Scott Hanselman, VP Developer Community, was able to compile images of these original discs and carefully scanned the original printed materials. While it hasn’t been possible to get our hands on the full MT-DOS Source code, MS DOS 4.00 is here and can now be found on Github, along with additional beta binaries, PDFs of the documentation and images of disk.
If you are interested in the discovery, know that you will need an original IBM PC XT machine, a more recent Pentium or use the open Source PCem and 86box emulators. Go to Github.
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