1ST1
Veteran Member
Microsoft has released the source code of MS-DOS 4.0(1) on Github. Also older versions previously released are there.
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