86-dos / pc-dos / tim paterson

Microsoft released what it calls the earliest DOS source code discovered to date: 86-DOS 1.00 kernel sources, development snapshots of PC-DOS 1.00, and utilities like CHKDSK, plus developer notes. The material predates the MS-DOS name and documents Tim Paterson’s original 86-DOS (QDOS) for the Intel 8086, which Microsoft licensed, developed further, and eventually bought before licensing it to IBM as PC-DOS while selling MS-DOS to other PC makers. Microsoft engineers Stacey Haffner and Scott Hanselman published the release. The archive is significant for historians, retrocomputing enthusiasts, OS researchers, and the software preservation community because it reveals early PC operating-system internals and the origins of a platform that shaped the PC industry.

The GitHub repository publishes transcriptions of Tim Paterson’s original DOS printouts, including the 86-DOS 1.00 kernel, PC-DOS pre-release kernels, utilities and Microsoft BASIC-86 runtime listings. The project has converted raw printer output into three downloadable sets: raw transcriptions, extracted printed files, and compilable source code (most targeting Seattle Computer Products’ ASM assembler and HEX2BIN). Bundles 1–8 have been transcribed; large Bundle 9 and Bundle 10 remain untranscribed and maintainers invite pull requests limited to direct transcription or typo fixes. The archive links, technical writeups, and assembly instructions make it possible to rebuild historical binaries, supporting software preservation and research into early PC OS development and licensing history.

GitHub hosts a transcription project of Tim Paterson’s original DOS printouts, converting 86-DOS 1.00 kernel, early PC-DOS pre-release kernels, utilities, and the Microsoft BASIC-86 runtime listings into compilable source. The repository offers three download bundles: raw transcriptions, extracted printed files, and ready-to-build source code; scanned originals are on Archive.org. The listing stack spans ten bundles (most transcribed except large bundles 9 and 10), with detailed file names and timestamps from 1981–1982. Contributors can submit pull requests to transcribe remaining pages or fix typos. Assembled sources target the Seattle Computer Products ASM and require HEX2BIN to produce binaries, enabling historical reconstruction and hands-on study of early PC DOS internals.

Microsoft has published scanned listings and transcriptions of 86-DOS 1.00 and PC-DOS 1.00 sources, including kernel snapshots and utilities like CHKDSK. The material — original assembler printouts and assembler listings discovered in Tim Paterson’s garage — illuminates early DOS development and provides a timeline of changes predating modern version control. Microsoft engineers Stacey Haffner and Scott Hanselman led the release, emphasizing the archival value of scanned code, notes, and analog artifacts from the late 1970s and early 1980s. While mainly of interest to retro computing enthusiasts and historians, the release offers lessons about compact, efficient coding and preserves primary artifacts of PC operating system origins. It complements last year’s MS-DOS 4.0 source release.