Microsoft open-sources "the earliest DOS source code discovered to date"
Recorded: May 24, 2026, 1:59 a.m.
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An IBM PC sitting next to old printed-out 86-DOS source code.
Text Story text Size Small Width Standard Links Standard * Subscribers only Minimize to nav Several times in the last couple of decades, Microsoft has released source code for the original MS-DOS operating system that kicked off its decades-long dominance of consumer PCs. This week, the company has reached further back than ever, releasing “the earliest DOS source code discovered to date” along with other documentation and notes from its developer. This source code is old enough that it hadn’t been stored digitally. “A dedicated team of historians and preservationists led by Yufeng Gao and Rich Cini,” calling itself the “DOS Disassembly Group,” painstakingly transcribed and scanned in code from paper printouts provided by Paterson. This process was made even more difficult because modern OCR software struggled with the quality of the decades-old printout. Andrew Cunningham Andrew Cunningham Andrew is a Senior Technology Reporter at Ars Technica, with a focus on consumer tech including computer hardware and in-depth reviews of operating systems like Windows and macOS. Andrew lives in Philadelphia and co-hosts a weekly book podcast called Overdue. 110 Comments Comments Forum view Loading comments... Prev story Next story Most Read 1. 2. 3. 4. 5. Customize Ars Technica has been separating the signal from More Contact Manage Preferences |
Microsoft has released the earliest discovered source code for the DOS operating system, establishing a deeper historical context for the development of MS-DOS. This release includes sources for the 86-DOS 1.00 kernel, several development snapshots of the PC-DOS 1.00 kernel, and known utilities such as CHKDSK, predating the formal MS-DOS branding. This historical material stems from the fact that programmer Tim Paterson originally created 86-DOS, previously known as QDOS, for an Intel 8086-based computer kit. Microsoft acquired the rights to 86-DOS and subsequently licensed it to IBM as PC-DOS, which Microsoft marketed as MS-DOS, leading to its widespread use among PC clones. The recovery of this foundational code was a painstaking process undertaken by a dedicated group of historians and preservationists known as the DOS Disassembly Group, led by Yufeng Gao and Rich Cini. They meticulously transcribed and scanned the source code from aging paper printouts provided by Paterson. This effort was complicated by the fact that modern optical character recognition software struggled to process the quality of the decades-old printouts. Beyond the earliest DOS source, Microsoft has engaged in open-sourcing several other early software projects. In 2014 and again in 2018, the company made open-source releases of MS-DOS versions 1.25 and 2.0, and further followed up in 2024 with the release of MS-DOS 4.0. These versions are hosted in the same repository on GitHub. Additionally, Microsoft has made other projects available, including the games Zork and its sequels, and the open-source remake of the old MS-DOS Editor, which represents a significant step in preserving early computing artifacts. |