Microsoft has released the source code for 86-DOS 1.00, the ancestor of Windows, as an open-source project on GitHub. The release marks the 45th anniversary of the original release of 86-DO, created by Tim Paterson, which would later be licensed to IBM as PC-DOS and later become MS-DOS. Microsoft has stated that these releases are intended to make historically significant system software accessible for study, preservation, and curiosity. A team of historians and preservationists led by Yufeng Gao and Rich Cini has found, scan, and transcribed the stack of DOS-era source listings from Paterson. The material also includes sources to the 86-D1.00 kernel, several development snapshots of the PC-OD 1.0 kernel, and some well-known utilities such as CHKDSK.