Support us on Patreon
PayPalFollowing on from officially open sourcing MS-DOS 4.0 back in 2024, Microsoft have announced more early DOS code has been made available.
The announcement today notes the code now includes sources for the 86-DOS 1.00 kernel, several development snapshots of the PC-DOS 1.00 kernel, and some well-known utilities such as CHKDSK. Microsoft said: "Not only were these assembler listings, but there were also listings of the assembler itself! This work offers rare insight into how MS-DOS/PC-DOS came to be, and how operating system development was done at the time, not as it was later reconstructed."
You also get some hand-written notes along with it, preserved directly by Tim Paterson (creator of 86-DOS). Microsoft's Scott Hanselman mentioned on Bluesky: "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".
Pretty cool for retro computing and preservation enthusiasts. Always nice to get another little look behind the curtain when it comes to older platforms.
See more in the Microsoft blog post and the GitHub.
Article taken from GamingOnLinux.com.
See more from me
You can also find comments for this article on social media: 
Still wondering what was so special that Microsoft could basically patent the CP/M filesystem.
Last edited by Ardje on 29 Apr 2026 at 5:08 pm UTC
Woodlandor 15 hours ago
Linux_Rocks 14 hours ago
Now if they wanna actually be cool, they'll open source all the way up to MS-DOS 6.22 and either open source Windows 3.11 or make it freely available on their site. They've got no money to lose in doing so and it'd just be easy PR for them.
Quoting: elmapulthe licence alllow to implement this on wine/proton/dosbox?I imagine FreeDOS is miles ahead of this ancient code. It's only interesting for historical purposes, especially with MS-DOS 4.0 also available.
hardpenguin 7 hours ago
Quoting: Phlebiacprobably, and probably that is why they relased it, to become "the heroes of preservation", when the truth is, we already had this.Quoting: elmapulthe licence alllow to implement this on wine/proton/dosbox?I imagine FreeDOS is miles ahead of this ancient code. It's only interesting for historical purposes, especially with MS-DOS 4.0 also available.
but still, there might be some conner cases where a few games or apps dont work and this solves it.
How to setup OpenMW for modern Morrowind on Linux / SteamOS and Steam Deck
How to install Hollow Knight: Silksong mods on Linux, SteamOS and Steam Deck