Microsoft has made MS-DOS source code available in GitHub. Back in March 2014, Microsoft released the source code to MS-DOS 1.25 and 2.0 via the Computer History Museum.
MS-DOS Source Code Is Available in GitHub
According to the Microsoft, They (re)published this file in GitHub to make them easier to find, help those people to use it more efficiently who are interested in early PC Operating Systems.
This repo of MS-DOS contains the original source-code and compiled binaries for MS-DOS v1.25 and MS-DOS v2.0.
Interesting point about MS-DOS
- All the source for MS-DOS 1.25 and 2.0 was written in 8086 assembly code
- The source code for the initial release of 86-DOS dates from around December 29th 1980
- The MS-DOS 1.25 code dates from around May 9th 1983, and is comprised of just 7 source files, including the original MS-DOS Command-Line shell – COMMAND.ASM!
- MS-DOS 2.0 dates from around August 3rd 1983, and grew considerably in sophistication (and team size), and is comprised of 100 .ASM files
- There are some interesting documentation (.TXT, .DOC) files interspersed with the source and object files – many are well worth a read, as are many of the source code comments!