Hacker News

Microsoft open-sources "the earliest DOS source code discovered to date"

87 points by DamnInteresting 3 hours ago | 22 comments

https://opensource.microsoft.com/blog/2026/04/28/continuing-...

jmward01 28 minutes ago

It is rare that I say this but, thanks MS! Arguably just as, if not more, important is the BASIC that they wrote. That was what they actually wanted to do. DOS just got them the contract with IBM. For decades MS was really a developer tools company with a side biz of writing operating systems and other misc software. They also open sourced that BASIC code too [1].

[1] https://opensource.microsoft.com/blog/2025/09/03/microsoft-o...

gnabgib 3 hours ago

Discussion, on the source, at the time (79 points, 24 days ago, 19 comments) https://news.ycombinator.com/item?id=47957494

Or on the GitHub clone (162 points, 15 comments) https://news.ycombinator.com/item?id=47946813

locusofself 2 hours ago

wow, they had to OCR it back in from paper printouts

> This source code is old enough that it hadn’t been stored digitally. “A dedicated team of historians and preservationists led by Yufeng Gao and Rich Cini,” calling itself the “DOS Disassembly Group,” painstakingly transcribed and scanned in code from paper printouts provided by Paterson. This process was made even more difficult because modern OCR software struggled with the quality of the decades-old printout.

FarmerPotato 25 minutes ago

I'd like to hear more about what works in OCR of dot-matrix fonts.

I've been able to OCR letter-quality printer output to 97% (mostly Os and Xs problems).

But it seems that machine-learning text-recognition is also now biased to reject computer code because it doesn't look like human language.

SoftTalker 2 hours ago

Yet another case where text printed on paper outlived any digital storage.

jshier 54 minutes ago

Seems like it was never digitally stored in the first place, and the printed text was barely readable due to age. Not really a big win for paper.

SoftTalker 44 minutes ago

Well it had to have been on disk or tape at some point. It wasn't all typed in by hand every time they needed to build a new version.

zargon 8 minutes ago

The idea that it never existed digitally is obviously untrue. Likely poor wording in the author's part. They probably meant something like, so old that a printout is all that survived (which sounds vaguely like not being digital to someone in an era so far removed from a time when programs were/could realistically be printed.)

petcat 40 minutes ago

> struggled with the quality of the decades-old printout.

barely

It sounds like this printout has deteriorated badly and was barely readable.

dang 3 hours ago

Recent and related:

Microsoft open sources DOS 1.00 on 45th anniversary - https://news.ycombinator.com/item?id=47957494 - April 2026 (19 comments)

dooosss 13 minutes ago

Too little, too late.

imoverclocked 2 hours ago

Time to find vulnerabilities!

I remember in the naughts, coming across a dos machine that was quite out of time… even for the university basement it was living in next to a pile of lead brick. Its only job was to run an instrument via an home-built ISA card and write data out to 5.25” floppies.

What uses would this code have in 2026?

FarmerPotato 28 minutes ago

To see what decisions they made. Like any historical document. Aim to understand the people of the time.

teamsolid 2 hours ago

It is wonderful how early years of modern computing was brilliant. We treated machines as they really are: machines. Performance, creativity, science..., all possible to make a 386 machine work. Nowadays is all about libraries, virtualization, [bad] code over [bad] code over [bad] code..., I dont like it.

dhosek 37 minutes ago

I sometimes think that my mental model of a computer is still an Apple ][+ with 48K of RAM leads to my writing better code.

userbinator 2 hours ago

I wonder how long it'll be before they release the source for the earliest Windows versions. The fact that they still have the source for this very old DOS at least gives hope that they also do for old Windows.

teamsolid 2 hours ago

I am sure that there is a lot good material to take inspiration and learning even from the early Windows 3.11.

mycall 58 minutes ago

Do a deep dive into how OS/360 formalized to having DOS.

SoftTalker 2 hours ago

/s ?

throwaway27448 39 minutes ago

They waited a couple decades too long for this to be of interest.

signa11 2 hours ago

in the words of mr. mitch-hedburg “here, you throw this away“

froyooh 2 hours ago

Back when it was all written by hand and optimized well.

xuzhenpeng 34 minutes ago

[flagged]