Several times over the past few decades, Microsoft has released the source code for the original MS-DOS operating system, ending its decades-long dominance of consumer PCs. This week, the company reached further back than ever, releasing “the oldest DOS source code ever discovered” along with other documents and notes from its developers.
Today’s source release is so old that it predates the MS-DOS branding, and includes “the sources of the x86-DOS 1.00 kernel, several development snapshots of the PC-DOS 1.00 kernel, and some well-known utilities”. CHKDSK“Write Microsoft’s Stacey Hafner and Scott Hanselman in their co-authored post about the release.
To understand the context, here’s a brief history of what would become MS-DOS: Programmer Tim Paterson originally created 86-DOS (formerly known as QDOS, for “Quick and Dirty Operating System”) for Intel 8086-based computer kits sold by Seattle Computer Products. Microsoft, ready to provide an operating system for the still-in-development IBM PC 5150, licensed 86-DOS and hired Patterson to continue developing it, later purchasing the rights to 86-DOS outright. Microsoft licensed this operating system to IBM as PC-DOS, while retaining the ability to sell the operating system to other companies. The version sold by Microsoft was called MS-DOS, and the proliferation of third-party IBM PC clones in the 80s and 90s made it the version of the operating system that most people came to use.
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