More retro goodies - Microsoft open sources 86-DOS and PC-DOS

Following 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.