Microsoft open-sources MS-DOS 1.0, offering a rare look at PC history

On the operating system's 45th anniversary, Microsoft has released the source code for 86-DOS 1.00, the first version of DOS for the IBM PC. The tech giant says that a dedicated team of historians and preservationists located, scanned, and transcribed the DOS-era source listing from Tim Paterson, the original creator of 86-DOS.

This listing includes the 86-DOS 1.00 kernel, development snapshots of the PC-DOS 1.00 kernel, and a few utilities you might recognize, including CHKDSK, offering an in-depth look at how DOS was created at the time.

Additionally, the listings take things a step further by including handwritten notes by Paterson, offering more context surrounding DOS' development, including timelines of changes, when features were implemented, and even errors and other issues. All of these artifacts will be on display at the Interim Computer Museum and have been donated by Paterson.

In 1980, Microsoft had the opportunity to build the operating system for IBM's PC, and then-CEO Bill Gates was tasked with delivering it on a tight timeline. Naturally, rather than develop an OS from scratch, Gates bought 86-DOS, also known as QDOS, from Seattle Computer Products and its creator, Tim Paterson, for roughly $75,000, setting Microsoft on the path to become the tech giant that it is today.

At the time, the OS ran on 160KB floppy disks and didn't feature hard-disk support, but it eventually became the foundation for what would eventually become MS-DOS, the dominant PC operating system of the 1980s and early 1990s. Before now, the earliest available versions of MS-DOS were 1.25 and 2.0.

"These releases are about making historically important systems software available for study, preservation, and plain ol’ curiosity," writes Microsoft's Stacey Haffner, the Director of Microsoft's OSPO and a developer advocate, and Scott Hanselman, VP and Member of Technical Staff at Microsoft/GitHub.

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