In March 2014, Microsoft released the source code to MS-DOS 1.25 and 2.0 via the Computer History Museum. The announcement also contains a brief history of how MS-DOS came to be for those new to the subject, and ends with many links to related articles and resources for those interested in learning more.

Today, we're re-open-sourcing MS-DOS on GitHub. Why? Because it's much easier to find, read, and refer to MS-DOS source files if they're in a GitHub repo than in the original downloadable compressed archive file.

Important: As noted on the repo readme, the source files are being (re)published for historical reference purposes and to allow exploration and experimentation for those interested in early PC Operating Systems. The source will be kept static, so please don’t send Pull Requests suggesting any modifications to the source files!

Some interesting things:

1. All the source for MS-DOS 1.25 and 2.0 was written in 8086 assembly code
2. The source code for the initial release of 86-DOS dates from around December 29th 1980
3. 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!
4. 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
5. 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!

Enjoy exploring the initial foundations of a family of operating systems that helped fuel the explosion of computer technology that we all rely upon for so much of our modern lives!

Source: Re-Open-Sourcing MS-DOS 1.25 and 2.0 Windows Command Line Tools For Developers

Posted By: Brink
30 Sep 2018