Microsoft Open-Sources DOS 1.0, Releasing Original Source Code and Annotations

Microsoft has open-sourced the original source code for PC-DOS 1.00, the operating system that launched the company toward its dominant position in personal computing. Before Microsoft became a household name, Bill Gates wrote BASIC interpreters and the company's first shipping operating system was a Unix distribution called Xenix. In 1980, IBM needed an operating system for its planned IBM PC and turned to Gates. Microsoft's AT&T Unix license did not allow porting Xenix to the x86 architecture, so the company purchased 86-DOS, also known as QDOS, from Seattle Computer Products and inventor Tim Patterson for just under $100,000. That purchase became the foundation for PC-DOS 1.00, which in turn led to MS-DOS and eventually Windows. The newly released code includes not only the original source but also annotations and historical context about the operating system's earliest days. Microsoft's open-source release provides researchers with a concrete reference point for the tangle of early DOS builds, version numbers, and OEM releases like MS-DOS 1.25. The company has continued to embrace open source in recent years, and this release offers a direct look at the software that helped establish Microsoft's place in computing history.