See The canonical version of this blog post on the Microsoft Open Source Blog!
Ten years ago, Microsoft released the source code for MS-DOS 1.25 and 2.0 to the Computer History Museum, and then I later republished them For reference purposes, this code holds an important place in history and is a fascinating read on an operating system that was written entirely in 8086 assembly code almost 45 years ago.
Today, in partnership with IBM and in the spirit of open innovation, we are releasing the source code for MS-DOS 4.00 under the MIT License. There is a somewhat complex and fascinating history behind the 4.0 versions of DOS, as Microsoft partnered with IBM to obtain parts of the code, but also created a branch of DOS called Multitasking DOS that was not widely distributed.
https://github.com/microsoft/MS-DOS
A young English researcher named Connor “Starfrost” Hyde Recently, he was contacted by Ray Ozzie, former technical director at Microsoft, about some of the software in his collection. Among the floppy disks, Ray found unreleased beta binaries of DOS 4.0 that had been sent to him while he was at Lotus. Starfrost contacted Microsoft’s Open Source Programs Office (OSPO) to explore the possibility of publishing the DOS 4 source code, as he is working on documenting 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 from Ozzie appear to be much older, unreleased, and also include source code from ibmbio.com.
Scott Hanselman, with the help of archivist and Internet enthusiast Jeff Sponaugle, has created images of these original disks and carefully scanned the original printed documents of this “Ozzie Drop.” Microsoft, along with our friends at IBM, believes this is a fascinating piece of operating system history worth sharing.
Jeff Wilcox and OSPO went to the Microsoft Archives and while they were unable to find the full source code for MT-DOS, they did find MS DOS 4.00, which we are releasing today, along with these additional beta binaries, PDFs of the documentation, and disk images. We will continue to explore the archives and may update this release if we discover more.
Thanks to Ray Ozzie, Starfrost, Jeff Sponaugle, Larry Osterman, our friends at IBM OSPO, as well as the creators of this digital archaeology software, including but not limited to Greaseweazle, Fluxengine, Aaru Data Preservation Suite, and the HxC Floppy Emulator. Most of all, thanks to the original authors of this code, some of whom still work at Microsoft and IBM today.
If you would like to run this software yourself and explore, we have successfully run it directly on an original IBM PC XT, a newer Pentium, and within the open source PCem and 86box emulators.
About Scott
Scott Hanselman is a former professor, former chief financial architect, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comedian, hair braiding expert, and author of books.
