Microsoft has released the 86-DOS 1.00 source code on GitHub to preserve computing history, giving developers and researchers rare access to the foundations of MS-DOS and Windows.
Microsoft has open-sourced the source code for 86-DOS 1.00 on GitHub, marking the 45th anniversary of the software and positioning the move as a digital preservation effort rather than a push for modern development.
The release carries deep historical significance. 86-DOS 1.00 served as the direct ancestor of MS-DOS and, by extension, Windows, and later formed the foundation of PC-DOS, which was licensed to IBM.
Originally developed by Tim Paterson, 86-DOS was acquired by Bill Gates and Microsoft for approximately $75,000 from Seattle Computer Products. Following modifications, it was delivered as PC-DOS 1.0 in August 1981.
The open-sourced material includes the 86-DOS 1.00 kernel, development snapshots of the PC-DOS 1.00 kernel, utilities such as CHKDSK, and even assembler listings and related tools, offering a rare, low-level view into early operating system development.
Microsoft stated that the release is intended to support study, preservation, and exploration of computing history. In its blog, the company noted: “Software history lives in code, yes, 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.”
The archival effort was supported by a team led by Yufeng Gao and Rich Cini, who worked to locate, scan, and transcribe original DOS-era materials.
Microsoft has previously open-sourced MS-DOS versions 1.25, 2.11, and 4.0, reinforcing its evolving approach to legacy software transparency.
