Microsoft Reopening MS-DOS 1.1 and MS-DOS 2.0 source code
Microsoft has announced the opening of the source code for the MS-DOS 1.1 and 2.0 operating systems released in 1982 and 1983. The code is open under the MIT license and is published on GitHub. The product is written in assembly language for 8086 processors.
It is noteworthy that the code was opened a second time, in 2014 original source texts were transferred to the Computer History Museum and became publicly available with a ban on use in commercial projects and distribution of copies on the Web. Now the license is changed to MIT, which allows you to freely make changes, distribute and use the code in your products.
https://github.com/Microsoft/MS-DOS
https://blogs.msdn.microsoft.com/commandline/2018/09/28/re-open-sourcing-ms-dos-1-25-and-2-0/
https://archive.org/details/github.com-Microsoft-MS-DOS_-_2018-09-29_01-14-23