The earliest DOS source code was found on printer paper in Tim Paterson's garage so we've open sourced it on 86-DOS 1.00’s 45th anniversary! This is next-level software archaeology for preservation, and plain ol’ curiosity. #DOS #RetroComputing

opensource.microsoft.com/blog/…

Continuing the story of early DOS development | Microsoft Open Source Blog

In 2018 we (re)-open-sourced MS‑DOS 1.25 and 2.11, and more recently in 2024 we were able to make the source for MS‑DOS 4.0 available to the public as well. Today, on 86-DOS 1.

^{Scott Hanselman (Microsoft Open Source Blog)}