GitHub - microsoft/MS-DOS: The original sources of MS-DOS 1.25, 2.0, and 4.0 for reference purposes
The original sources of MS-DOS 1.25, 2.0, and 4.0 for reference purposes - microsoft/MS-DOS
github.com
FWIW the source code for 1.25 & 2.0 has been up on Github for probably about 6 or so years now. It was 4.0 that just got uploaded to the repository yesterday.Its mentioned in the readme that they released the sourcecode originally to the computer history museum back in 2014.