As a continued effort to preserve some of the oldest computing artifacts, such as the UNIX 4th Edition tape discovery that happened as 2025 was coming to the end, Microsoft has continued to give access to the source code of old versions of MS-DOS, such as version v1.25 and v2.11.

Today, on April 28th, Microsoft has made a huge announcement that will excite those interested in retrocomputing in a way that never happened before. Microsoft has finally released the source code of the earliest DOS versions discovered!

You can see the GitHub page of the source code here.

Those newly-available source code materials that provide an early look of how PC-DOS 1.0, the first DOS for IBM PCs, was developed, as a celebration of the 45th year anniversary of the antique operating system. This collection of such materials, such as e-mails and other documents, were done by a team of historians and preservationists, with the leaders being Yufeng Gao and Rich Cini.

The team has located, scanned, and transcribed the stack of DOS-era source listings from the author of DOS, Tim Patterson, which are now available in the MS-DOS source code found on GitHub. Those listing include interesting bits, such as development snapshots of the PC-DOS 1.0 kernel, sources to 86-DOS 1.0 kernel, and utilities like CHKDSK, a program for checking your disk for errors.

https://twitter.com/shanselman/status/2049171077079998908

This is such a huge discovery and preservation that was done, and anyone who’s interested in seeing those artifacts in person will be able to do so by visiting the Interim Computing Museum in the next coming days.

To learn more, visit this announcement post: