Microsoft in cooperation with IBM, released the source code for MS-DOS 4.0 under the MIT Open License and following the release of MS-DOS 1.25 and 2.0 code that occurred several years ago. The publication of this type of code serves as a historical reference, enabling research and experimentation for interested researchers the first PC operating systems and also as a discovery for developers and restless users as this software can be run on emulators or old machines for those lucky enough to have access to one of these.

They say so from Microsoft’s open source blog “behind MS-DOS 4.0 is a complex and fascinating history”, because the Redmond firm worked with IBM to create parts of the code, but also created a branch of DOS called Multitasking DOS that was not released to the general public. In this article, they tell us the story of their liberation.

A young English researcher, Connor “Starfrost” Hyde, recently contacted former Microsoft CTO Ray Ozzie about some of the programs in his collection. Ray found among the floppy disks unreleased DOS 4.0 beta binaries that they sent him while he was in Lotus.

Working to document the relationship between DOS 4, MT-DOS, and what would eventually become OS/2, Starfrost contacted the Microsoft Open Source Programs Office (OSPO) to explore the possibility of releasing the MS-DOS 4.0 source code. Some later versions of these multitasking DOS binaries can be found on the internet, but these new Ozzie beta binaries were much older, unreleased, and also included the ibmbio.com source.

Vice President of the Microsoft Developer Community, Scott Hanselman, with the help of archivist and enthusiast Jeff Sponaugle, created a rendering of these original discs and meticulously scanned the original printed documents Ozzie. Meanwhile, the head of open source programs, Jeff Wilcox, “dived” into the Microsoft Archives, and although he could not find the complete source code for MT-DOS, they found MS DOS 4.00.

And finally, thanks to further cooperation with IBM employees the publication of the MS-DOS 4.0 source code under the MIT Open License has ended, along with additional beta binaries, documentation PDFs, and disc images. next Mrfascinating piece the history of the operating system launched into orbit by the unknown Microsoft (including conspiracy theory) and served as the basis for the transition to graphical interfaces with Windows 95.

If you want to try this softwaresay they ran it directly on an original IBM PC All MS-DOS 4.0 material is freely available on its GitHub page.