Microsoft releases the earliest DOS source code ever discovered as open source

Microsoft has released the earliest known DOS-related source material, including 86-DOS and early PC-DOS listings, notes, and build files.

The repository offers rare primary-source insight into how early PC operating systems were designed and built.

The release continues Microsoft’s software preservation efforts and documents the origins of MS-DOS and the broader PC era.

Researchers, developers, and digital historians can use the archive for study, compatibility work, and historical context.