Microsoft open-sources earliest DOS source code discovered
Original: Microsoft open-sources “the earliest DOS source code discovered to date”
Why This Matters
Preserves foundational PC operating system history that launched Microsoft's dominance
Microsoft released source code for 86-DOS 1.00 kernel, predating MS-DOS branding. Code was transcribed from paper printouts by historians and preservationists led by Yufeng Gao and Rich Cini, representing the earliest DOS source code discovered to date.
Microsoft open-sourced the earliest DOS source code discovered, including 86-DOS 1.00 kernel sources, PC-DOS 1.00 development snapshots, and utilities like CHKDSK. The code predates MS-DOS branding and was originally created by Tim Paterson for Seattle Computer Products' Intel 8086-based computer kit. Microsoft licensed 86-DOS for the IBM PC 5150, hired Paterson, then bought the rights outright. The company sold it to IBM as PC-DOS while retaining rights to license as MS-DOS to other manufacturers. The source code wasn't stored digitally and required manual transcription from paper printouts by the DOS Disassembly Group. Microsoft previously open-sourced MS-DOS versions 1.25, 2.0, and 4.0 in 2014-2024.