Microsoft has made the source code for 86-DOS 1.00 available on GitHub to celebrate its 45th anniversary. 86-DOS, developed by Tim Paterson, was foundational for MS-DOS and Windows. This release is part of Microsoft's effort to preserve historically significant software. Microsoft previously released the source code for MS-DOS versions 1.25, 2.11, and 4.0. A team of historians and preservationists has gathered and transcribed DOS-era source listings, including the 86-DOS 1.00 kernel and development snapshots of the PC-DOS 1.00 kernel. Microsoft acquired 86-DOS from Seattle Computer Products for approximately ,000 and modified it to deliver PC-DOS 1.0 in August 1981, which became known as MS-DOS for IBM-compatible computers.