# 86-DOS 1.00 and PC-DOS 1.00 Source Listings (Paterson Listings) On 86-DOS 1.00's 45th anniversary (April 2026), Microsoft's Open Source blog announced that the [DOS-History/Paterson-Listings](https://github.com/DOS-History/Paterson-Listings) repository — a multi-year recovery effort led by historians [Yufeng Gao](https://thebrokenpipe.com/about/) and [Rich Cini](http://cini.classiccmp.org/) — has been licensed under MIT through a coordinated pull request. The listings come directly from Tim Paterson's personal archive and are now publicly available for study. This sits alongside the earlier MS-DOS 1.25/2.0 (2018) and MS-DOS 4.0 (2024) source releases as part of Microsoft's incremental opening of early DOS history. ## What's in the listings - The **86-DOS 1.00 kernel** — Paterson's original 8086 OS, written at Seattle Computer Products before IBM picked it for the PC. This is the actual ancestor of MS-DOS, not a later reconstruction. - Several **development snapshots of the PC-DOS 1.00 kernel** — point-in-time working states preserved on paper as the IBM PC release was assembled. - Well-known utilities including **CHKDSK**. - Listings of the **assembler itself** — DOS-era development tooling, not just the OS. The listings are assembler printouts with hand-written notes by Paterson preserved alongside the code. The Microsoft post frames them as "a printed commit history of a Git repository" — each listing captures the code at the moment it was printed, which features were implemented when, what errors were made, and how they were fixed. That kind of point-in-time view of development is rare for systems software of this era. ## How the recovery happened This wasn't a simple "scan a few documents" effort: - **Locating the source** — Tim Paterson kept his archive of printouts. Recovery required convincing him to share, then physically transporting the materials. - **Scanning** — multi-thousand-page assembler printouts in their original physical form. - **OCR'ing** — printer listings of dense assembly are notoriously hard for off-the-shelf OCR. Joshua Carsbrook ([jscarsbrook.me/doshistory/](https://jscarsbrook.me/doshistory/)) developed printer-listing-specific OCR for this work. - **Transcription and validation** — turning OCR output into compilable assembler. - **Legal review** — the MIT licensing required a pull request coordinated with Microsoft's open source program office. The physical artifacts have since been donated by Tim Paterson to the [Interim Computer Museum](https://icm.museum/). ## Why this matters This is the earliest DOS source code anyone has yet recovered — predating the 1.25 release by about a year. For studying how operating systems were built in 1980-1981 (development practices, hand-edited code paths, the assembler ecosystem), the printed listings are a primary source the way committed git history would be for a modern codebase. They show what shipped *and* what was tried and rejected, in Paterson's own annotations. The MIT license is the load-bearing detail for hobbyists, retro-computing projects, and emulator authors who want to use, port, or study the code without a research-only restriction. ## Related - [[sdl3-dos-port]] — modern SDL3 native DOS support via DJGPP, also from April 2026 — same retro-DOS-in-2026 thread - [[dosbox-detection-callback-opcode]] — Snow's December 2025 post on detecting DOSBox via the custom-invented `FE 38 00 00` callback opcode - DOS-History/Paterson-Listings: - Yufeng Gao's writeup: - Rich Cini's recovery blog: