Microsoft open-source “the original DOS code available to date”

Several times over the past few decades, Microsoft has released the source code for the MS-DOS operating system that led to its decades-long dominance of consumer computers. This week, the company did it has come further than beforereleasing “the original DOS code found to date” along with other documentation and notes from the developer.

Today’s source code is so old that it predates MS-DOS, and includes the “86-DOS 1.00 kernel source code, several development images of the PC-DOS 1.00 kernel, and other well-known sources such as CHKDSK,” wrote Microsoft’s Stacey Haffner and Scott Hanselman in a statement they co-wrote about the release.

To understand what’s going on, here’s a very brief history of what would become MS-DOS: Programmer Tim Paterson originally developed 86-DOS (formerly known as QDOS, for “quick and dirty system”) on an Intel 8086 computer sold by Seattle Computer Products. Microsoft, on the hook to provide operating systems The IBM PC 5150 that is still aroundlicensed 86-DOS and recruited Paterson to continue development, then purchased the rights to 86-DOS directly. Microsoft then licensed it to IBM as PC-DOS and retained the ability to sell the system to other companies. The version sold by Microsoft is called MS-DOS, and the proliferation of third-party IBM PC systems in the 80s and 90s made it the operating system most people used.