Microsoft has released the source code for 86-DOS 1.00 as an open-source project on GitHub [1, 2].
The move preserves the foundation of the modern personal computing era. By making the ancestor of Windows available to the public, Microsoft allows software historians and developers to study the architecture that powered the first IBM PCs.
The release includes more than just the raw code. Microsoft published handwritten notes and assembler listings that were preserved for over 40 years [2]. These documents provide a rare glimpse into the manual processes of early software engineering, and the logic used by the original developers.
Tim Paterson, the original author of 86-DOS, and various software historians contributed to the effort [1, 2]. The project is hosted at github.com/microsoft/86-DOS, where the community can now access the materials [1, 2].
Microsoft said the project was launched to commemorate the 45th anniversary of the operating system [1]. The company intends to preserve this piece of computing history for the open-source community [1, 2].
86-DOS served as the basis for MS-DOS, which in turn became the platform for early versions of Windows. The availability of these files allows researchers to trace the evolution of disk operating systems and the transition from assembler language to higher-level programming. Because the materials include original notes, they offer a narrative of the development process that code alone cannot provide.
“Microsoft released the source code for 86-DOS 1.00, including handwritten notes and assembler listings.”
This release transforms a proprietary corporate asset into a historical archive. By open-sourcing 86-DOS, Microsoft acknowledges the collaborative and iterative nature of early computing, providing a primary-source blueprint for how the industry shifted toward the standardized operating systems that defined the 1980s and 1990s.
