Microsoft Open-Sources Early MS-DOS Versions, This Time to GitHub

Posted on October 2, 2018 by Paul Thurrott in Dev, Microsoft with 9 Comments

Microsoft this week announced that it has “re-open-sourced” MS-DOS 1.25 and 2, this time to GitHub. The releases follow any earlier open-sourcening, ahem, via the Computer History Museum in 2014.

“We’re re-open-sourcing MS-DOS on GitHub because it’s much easier to find, read, and refer to MS-DOS source files if they’re in a GitHub repo than in the original downloadable compressed archive file,” Microsoft’s Rich Turner explains. “The source files are being (re)published for historical reference purposes and to allow exploration and experimentation for those interested in early PC operating systems [only].”

That last bit refers to the fact that GitHub is often used for open-source projects where others can make “pull requests,” which are suggestions for modifications. Obviously, Microsoft has no intention of modifying this code.

The MS-DOS source code was written entirely in 8086 Assembly Language and dates back to 1980. So you’ll want to fire up your dusty copy of MASM while strolling done memory lane.


Tagged with

Join the discussion!


Don't have a login but want to join the conversation? Become a Thurrott Premium or Basic User to participate

Comments (9)

9 responses to “Microsoft Open-Sources Early MS-DOS Versions, This Time to GitHub”

  1. dstrauss

    Any chance they'll bring back the PC Jr. and eight track tapes at today's "Moment" event? Sorry, just couldn't resist - my bad.

  2. wright_is

    That would be 8088 / 8086 assembler. ;-)

    It makes interesting reading, although I grew up on Z80, 6502, DEC Macro and Motorola 68000 assembler, the 6502 and especially 68000 were designed for programmers, the x86 assembler is much more programmer hostile.

  3. MikeGalos

    I read a lot of the code when it was first released and it was fascinating to read the comments.

  4. skane2600

    I can't comment directly on the Premium side but I concur with "wright_is", that 8088/86 was a terrible CPU for programmers. The lack of a linear address space arguably created a 10% or more hit on software development efficiency. One wonders if the Mac would have been created at all if Apple had used the 8086 rather than a 68000.

  5. jimchamplin

    Will it build? ?

  6. cwfinn

    I'm still running MS-DOS 2.2 on my HP95LX with Lotus 123 built into ROM! Now I can see the source code! ;)

  7. jil789r

    For those of you who share my passion for all DOS games you might wanna check out , tons of DOS based games , ZX, commodore 64.