Microsoft open-sources MS-DOS 4.0.
And there's an interesting writeup to go with it.
Today, in partnership with IBM and in the spirit of open innovation, we’re releasing the source code to MS-DOS 4.00 under the MIT license. There’s a somewhat complex and fascinating history behind the 4.0 versions of DOS, as Microsoft partnered with IBM for portions of the code but also created a branch of DOS called Multitasking DOS that did not see a wide release.
![](https://cloudblogs.microsoft.com/opensource/wp-content/uploads/sites/37/2024/04/Azure_Blog_Abstract-01_1260x708-social.jpg)