A decade after releasing the source code for MS-DOS 1.1 and MS-DOS 2.0, Microsoft has open sourced a (slightly) more recent operating system: MS-DOS 4.0.
First released in 1988, you can now download the source code from GitHub, where it’s been shared under the MIT license.
Of course there’s not much reason to actually run MS-DOS on anything other than a decades-old computer at this point, but Microsoft’s Scott Hanselman and Jeff Wilcox are positioning this as a release for educational purposes: it’s a way to preserve a bit of computer history and allow folks who are interested in learning about the earlier days of personal computing to examine the code.
This release is also interesting because it doesn’t just include include MS-DOS 4.0, which was widely available in the late 1980s, but also code and documentation for an early version of “a branch of DOS called Multitasking DOS that did not see a wide release.”
That MT-DOS code comes from former Microsoft CTO Ray Ozzie, who recently found some floppy disks with the code while corresponding with English researcher Connor “Starfrost” Hyde, who is working on documenting the history of MT-DOS.
Microsoft says it’s possible to run the software in this release “on an original IBM PC XT, a newer Pentium,” or with emulators like PCem and 86box.
I dream abou mac os 6 or 7
make a petition
@boxy thanks for bringing up Free DOS, I was going to mention it myself. The only reason I could see to be interested is in this release of the MS DOS 4.0 source code would be for historical preservation of the code and to hopefully keep Microsoft interested in continuing to release more of their source code, even if it’s for ancient technology.
Otherwise I don’t see much more reason to be excited for this, considering that we already have Free DOS.
Is there an advantage to running this MS-DOS 4.0 over FreeDOS?
No, none. MS-DOS 4.0 is too old and buggy; 6+ if you really need it, otherwise FreeDOS is the way to go.