MS-DOS 4.0 source code release: What a story!

After versions 1.25 and 2.0, the source code for MS-DOS v4.0 has just been published online under the MIT License by Microsoft, in cooperation with IBM. And it's not just any version of MS-DOS 4. Explanations.

in March 2014Microsoft turned over the source code for MS-DOS 1.25 and 2.0 to the Computer History Museum and then released them to Reference on GitHub. This same account will now host a specific version of MS-DOS 4.00 under the MIT License.

We owe this discovery to an English researcher, Connor “Starfrost” Hayden,software collector. Among the floppy disks he had were unpublished beta binaries of DOS 4.0, sent to him while he was still working at Lotus.

What's so fascinating is the winding history of versions 4.0 of DOS: Microsoft actually collaborated with IBM for parts of the code, but it also created a fork of DOS called DOS Multitaskingwhich is not widely distributed.

Incidentally, Starfrost chose to contact Microsoft's OSPO subsidiary to explore the possibility of releasing the source for DOS 4, as it was working to document the relationship between DOS 4, MT-DOS, and what would eventually 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 Software Office, On the publisher's blog.

Scott Hanselman, Vice President of the Developer Community, was able to compile images of these original discs and carefully scan the original print materials. Although it has not been possible to obtain the full MT-DOS source code, MS DOS 4.00 is here and can now be found on Github, along with additional beta binaries, documentation PDFs, and disk images.

If you're interested in exploring, know that you'll need an original IBM PC XT machine, a newer Pentium machine, or use the open source PCem and 86box emulators. Go to GitHub.