Microsoft opens door to the past by releasing 86-DOS and PC-DOS 1.00
- Reference: 1777464835
- News link: https://www.theregister.co.uk/2026/04/29/microsoft_pc_dos_1_point_oh/
- Source link:
The [1]release comes a year after Microsoft set the [2]source for MS-DOS 4.0 free, but it includes a lot more than just the bones of an old operating system.
According to a post by Microsoft's Stacey Haffner and Scott Hanselman, "The listings include sources to the 86-DOS 1.00 kernel, several development snapshots of the PC-DOS 1.00 kernel, and some well-known utilities such as CHKDSK."
[3]
"Not only were these assembler listings, but there were also listings of the assembler itself!"
[4]
[5]
It is quite the treasure trove of information, and a throwback to an era when printouts were your friend for storing source code. "Software history lives in code, yes," acknowledged the pair, "but also in scanned listings, internal documents, assembler printouts, and the sometimes wonderfully analog artifacts of how operating systems came together in the late 1970s and early 1980s."
In a post on Bluesky, Hanselman [6]wrote , "The earliest DOS source code was found on printer paper in Tim Paterson's garage."
[7]
The printout predates tools like GitHub by decades. Where a Git repository might have a commit history, the printouts "create a timeline of changes, showing which features were implemented when, what errors were made, and how they were fixed."
[8]How CP/M-86's delay handed Microsoft the keys to the kingdom
[9]US and Europe try to tame surveillance capitalism
[10]Code archaeologist digs up oldest known ancestor of MS-DOS
[11]Infosys founder slams working from home, side hustles, as slowing India's growth
86-DOS was released in 1980 and was the brainchild of Tim Paterson. Microsoft licensed it and eventually purchased all rights in 1981, shortly before the release of the IBM PC. [12]Various lawsuits were launched in subsequent years over the deal, and some alleged similarities to CP/M, but the key thing here is the insight the material provides into the development of PC-DOS 1.00.
Hanselman, Haffner, and the rest of the team behind the release are to be commended for their effort in dusting off the source and painstakingly scanning in and transcribing a stack of Paterson's printouts and notes.
How much practical use the first version of DOS will have outside the retro enthusiast community is debatable, though it is a fascinating insight into how the operating system came to be and highlights a time when code was crammed into the smallest space possible, while retaining utility and efficiency.
Lessons for modern programmers, then, as well as an invaluable resource for IT historians. ®
Get our [13]Tech Resources
[1] https://opensource.microsoft.com/blog/2026/04/28/continuing-the-story-of-early-dos-development/
[2] https://www.theregister.com/2024/04/26/ms_dos_4_open_source/
[3] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_software/oses&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=2&c=2afIrH1IHIJF6HoqmcilR1wAAAMw&t=ct%3Dns%26unitnum%3D2%26raptor%3Dcondor%26pos%3Dtop%26test%3D0
[4] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_software/oses&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=4&c=44afIrH1IHIJF6HoqmcilR1wAAAMw&t=ct%3Dns%26unitnum%3D4%26raptor%3Dfalcon%26pos%3Dmid%26test%3D0
[5] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_software/oses&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=3&c=33afIrH1IHIJF6HoqmcilR1wAAAMw&t=ct%3Dns%26unitnum%3D3%26raptor%3Deagle%26pos%3Dmid%26test%3D0
[6] https://bsky.app/profile/scott.hanselman.com/post/3mkl2kqvxqc2d
[7] https://pubads.g.doubleclick.net/gampad/jump?co=1&iu=/6978/reg_software/oses&sz=300x50%7C300x100%7C300x250%7C300x251%7C300x252%7C300x600%7C300x601&tile=4&c=44afIrH1IHIJF6HoqmcilR1wAAAMw&t=ct%3Dns%26unitnum%3D4%26raptor%3Dfalcon%26pos%3Dmid%26test%3D0
[8] https://www.theregister.com/2026/01/12/why_cpm86_was_late/
[9] https://www.theregister.com/2024/03/05/us_europe_capitalism/
[10] https://www.theregister.com/2024/01/05/oldest_ancestor_of_msdos_recovered/
[11] https://www.theregister.com/2023/02/27/asia_tech_news_roundup/
[12] https://www.theregister.com/2007/07/30/msdos_paternity_suit_resolved/
[13] https://whitepapers.theregister.com/
Antiques code show
As someone from the UK it is worth one of these just for the header ->
I miss the early days of personal computing, when everything was new and presented so many opportunities to learn, discover, and create - usually all at the same time.
And the ensuing multitudes of machines and operating systems, and trying to rewrite code to work on different platforms.
And a half-dozen friends and colleagues all gathered around one computer, chiming in with corrections and suggestions late into the night.
And taking turns raiding the refrigerator or the corner store, falling asleep wherever it was convenient, being awakened by colleagues cheering success or decrying mistakes and failures.
And doing it all over again.
It used to be fun, and personal, and rewarding. Now it's just another job.
Sic Transit Gloria Mundi.
The problem is not lack of variety now, is you/me/w'all getting older.
We have MIPS (yes, MIPS is still viable, from embedded to supercomputers, if you want it), OpenSPARC, OpenPOWER, ARM, X86 and RISC-V all vying for yor attention. If you want to port, port.
Then we have Linux (in 600+ distro flavours), *BSD (in like 5 or 6 Flavours), MacOS (based on BSD, but with so much propiertary stuff on top as to warrant a separate entry), Windows, AIX and Slowlaris/SunOS. Or, if you want to go small, there are also a plethora of RT-OSs, some of them with WMs/DEs , if that's your fancy. If you want to port, port.
Plenty of different platforms to re-write code for. Plenty of opportunities to gather around one computer if that's your fancy, or to unbound your circle of coding friends from geography, and do a hackathon over teamspeak*.
Thing is we became old and jaded. And we have other resposabilities, and other preferences...
I hope the kids are enjoying the current variety as much as we did back then.
* anachronistic choice intentional.
I wonder if they'll mistakenly release a version that includes CP/M headers?
86-DOS
Somebody indict that trademark.
DOS 4
Hopefully this time round they won't make the same mistake as they made with releasing the DOS 4 source code.