In March 2014, Microsoft had released the source code to MS-DOS 1.25 and 2.0 via the Computer History Museum. A few days ago, they have re-released that same source on GitHub so it's much easier to find. Microsoft encourages exploring and experimenting with the source, but ask people not to send Pull Requests, as this publishing is purely for historical purposes.
You can check out MS-DOS on GitHub here.

Source - Microsoft Developer Blog
Coverage of the original release 4 years ago by FAST6191

 

[Deleted User]

Saw this on Github hours ago and wondered how it wasn't on the front page yet. This is pretty important news imo.

 

[lolboy]

Asm...Respect for those whom can code in Asm

 

[Sheimi]

Asm...Respect for those whom can code in Asm

I can code in asm

 

[lolboy]

I can code in asm

Respect. For what purpose did you learn Asm?

 

[Subtle Demise]

468 lines of code for CTRL+C. Really makes you appreciate the kind of work that goes into these kinds of things.

 

[AboodXD]

Should have included a link to the GitHub repository...

 

[smileyhead]

Should have included a link to the GitHub repository...

Added the link to the bottom of the post.

 

[ry755]

The GitHub issues are amazing

 

[ShadowOne333]

This is it, folks.
Time to start working on MS-TRES

 

[matpower]

Saw this on Github hours ago and wondered how it wasn't on the front page yet. This is pretty important news imo.

Not really, first it was released 4 years ago, just somewhere else, and we have had FreeDOS for almost two decades now, whoever wants to see how DOS works can check FreeDOS' source code. Furthermore, MS-DOS 2.x is too old to be of any help to projects such as FreeDOS (which is 99.9% percent compatible, except with an edge case involving Windows 3.11).

 

[souhukyafod]

Time to MesS around with DOS lines!

 

[Akdul]

This made me nostalgic, I loved this OS as a kid. Btw, you can play lots of DOS games directly in your browser here. There are lots of gems in there:

https://archive.org/details/softwarelibrary_msdos_games

 

[souhukyafod]

This made me nostalgic, I loved this OS as a kid. Btw, you can play lots of DOS games directly in your browser here. There are lots of gems in there:

https://archive.org/details/softwarelibrary_msdos_games

Also with other emulators along with website archives. Archive.org is amazing.

 

[Taleweaver]

Saw this on Github hours ago and wondered how it wasn't on the front page yet. This is pretty important news imo.

Erm... Sorry, but I'm not seeing why. It was released in 2014 already, and it's not like they're releasing the source codes of newer versions (just checked : it went up to 7.0). And even then... What's the practical use? Github is certainly better for sharing and updating but why would you want it?

 

[Akdul]

Also with other emulators along with website archives. Archive.org is amazing.

Yeah, Archive.org is great. Speaking about DOS games, I wanted to recommend this hidden DOS gem, it's an awesome racer/platformer game. I spent hours playing that as a kid, good times.

https://archive.org/details/SkyRoads

 

[Alato]

Seeing that MS-DOS logo brings back some memories-

Yeah, Archive.org is great. Speaking about DOS games, I wanted to recommend this hidden DOS gem, it's an awesome racer/platformer game. I spent hours playing that as a kid, good times.

https://archive.org/details/SkyRoads

Totally, SkyRoads is easily one of my favorites. Loved the music, too.

Laser Light was another one of my favorites: https://archive.org/details/msdos_Laser_Light_1994

 

[souhukyafod]

Yeah, Archive.org is great. Speaking about DOS games, I wanted to recommend this hidden DOS gem, it's an awesome racer/platformer game. I spent hours playing that as a kid, good times.

https://archive.org/details/SkyRoads

I feel like I've played this game before. Or maybe clones.
The sound is on top and I really like its visual technique.

 

[DinohScene]

Saw it yesterday, neat! Now for Win 98 : D

 

[Clydefrosch]

Will this improve DOSbox or make it easier to port or is all of this basically already known?