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

 

[Sheimi]

Respect. For what purpose did you learn Asm?

I originally learned it for Sonic hacking. Now I do it for knowledge.

 

[FAST6191]

Ahh the good old days of typing multiple lines of directories, and failing at least twice, just to boot up Duke Nukem 3D.

Thank the Lord that's over I hated it.

What kind of scrub does not reboot their computer with their chosen game's custom boot disc in it?

 

[Ryccardo]

I always forget that MS-DOS doesn't have tab completion or command history

Command.com doesn't, that's Doskey's job - or just use an alternative shell like 4DOS!

 

[Captain_N]

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

I have respect for asm coders. Think of all the NES and SNES games coded that way.... The music was coded that way. And look what they did with such limitations.... Now devs just use pre-made engines and slap their assets on it... Oh and the shit does not even have to work well because they can just patch it.

 

[MaybeTheLastBilly]

Why didn't they release the other versions of DOS while they're at it? I mean, I dont think any of them could have something relevant nowadays...

 

[Ryccardo]

Why didn't they release the other versions of DOS while they're at it? I mean, I dont think any of them could have something relevant nowadays...

Actually they still sold 6.22 until earlier this decade
And technically, they are still selling a DOS and Win16 compatibility layer (as part of every 32-bit Windows to date)...

...I guess they don't want to look "TOO" giveaway-y?

 

[MaybeTheLastBilly]

Actually they still sold 6.22 until earlier this decade
And technically, they are still selling a DOS and Win16 compatibility layer (as part of every 32-bit Windows to date)...

...I guess they don't want to look "TOO" giveaway-y?

LOL really? Well in that case I guess it makes sense... I just wanted to play doom on an open-source version of DOS

 

[WildDog]

LOL really? Well in that case I guess it makes sense... I just wanted to play doom on an open-source version of DOS

You could play Doom on Open Source Dos for a long time. FreeDOS is not exactly new.

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

Not really, plus for what is DOSbox and the Svn builds are much "perfected". You can pretty much play most of the games.
If you have a nice PC or laptop and want something more accurate then you use 86box or PCem.

Like other posters said, this is more for historic purpose.

 

[matpower]

LOL really? Well in that case I guess it makes sense... I just wanted to play doom on an open-source version of DOS

FreeDOS, a GPL licensed DOS implementation, is already 20 years old and it is 99.9% compatible. Only Windows 3.x doesn't work properly, but it doesn't work anywhere else but MS-DOS.
It is an outstanding project and you should check it out at least once.

 

[the_randomizer]

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

Isn't ASM an absolute hellish nightmare to learn?

 

[ry755]

Isn't ASM an absolute hellish nightmare to learn?

Yeah. It's not too bad if you take it step by step though

 

[the_randomizer]

Yeah. It's not too bad if you take it step by step though

Looking at ASM makes my head spin

 

[ry755]

Looking at ASM makes my head spin

Guess what this does:
https://gbatemp.net/threads/what-happens-when-a-programmer-is-bored.519779/

 

[the_randomizer]

Guess what this does:
https://gbatemp.net/threads/what-happens-when-a-programmer-is-bored.519779/

No idea, sorry

 

[ry755]

No idea, sorry

It prints "Hi guys. As you can see, I'm bored!"
Because no one with any sanity would program in asm

 

[FAST6191]

Isn't ASM an absolute hellish nightmare to learn?

Compared to a lot of languages today it is harder but you can still get useful results, to say nothing of learning assembly to a reasonable level will tend to help you write better code*. If you stick with the really old stuff from back when it will probably be a nightmare but the modern world and all the debug tools it affords means we have stuff like http://www.plantation-productions.com/Webster/HighLevelAsm/index.html and https://stuff.pypt.lt/ggt80x86a/asm1.htm which for me at least made it quite manageable. Those will cover x64/x86, if you want something else for an embedded system then look up whether such a thing was used in a console for ROM hackers then tend to have nice tools and documentation. Mind you it has been said learn one assembly and you are good, learn two and you can pretty much understand them all -- some will have quirks, some will have fewer abilities (some really old chips not only lack divide but subtraction is tricky) and slightly different syntax** but in the end it is still going to be the same handful of arithmetic instructions, device management instructions and program flow instructions that you use day in and day out.

*classic example being if you write a function call in assembly you will understand very clearly why calling a function within a function in C, or indeed most other languages, is not ideal.

**something like the NES 6502 only has three registers used in general use so most people consider individual instructions for them. To do that with the dozens of registers on the average x86 processor would be madness so people instead consider instructions as things and just fill in source and destination.

 

[the_randomizer]

Compared to a lot of languages today it is harder but you can still get useful results, to say nothing of learning assembly to a reasonable level will tend to help you write better code*. If you stick with the really old stuff from back when it will probably be a nightmare but the modern world and all the debug tools it affords means we have stuff like http://www.plantation-productions.com/Webster/HighLevelAsm/index.html and https://stuff.pypt.lt/ggt80x86a/asm1.htm which for me at least made it quite manageable. Those will cover x64/x86, if you want something else for an embedded system then look up whether such a thing was used in a console for ROM hackers then tend to have nice tools and documentation. Mind you it has been said learn one assembly and you are good, learn two and you can pretty much understand them all -- some will have quirks, some will have fewer abilities (some really old chips not only lack divide but subtraction is tricky) and slightly different syntax** but in the end it is still going to be the same handful of arithmetic instructions, device management instructions and program flow instructions that you use day in and day out.

*classic example being if you write a function call in assembly you will understand very clearly why calling a function within a function in C, or indeed most other languages, is not ideal.

**something like the NES 6502 only has three registers used in general use so most people consider individual instructions for them. To do that with the dozens of registers on the average x86 processor would be madness so people instead consider instructions as things and just fill in source and destination.

I've thought about delving into programming, but never found the motivation to do so, or even where to start.

 

[ry755]

I've thought about delving into programming, but never found the motivation to do so, or even where to start.

Python is a good language to start with. There's lots of good guides online

 

[Song of storms]

How did I miss this news? This is amazing!