On the 45th anniversary of the debut of 86-DOS 1.00, Microsoft has archived and made public the earliest known DOS source code, adding to its growing collection of classic operating systems that have been progressively open-sourced in recent times. These released resources are of immense historical importance, encompassing kernel source code, utility programs, and listings of assembler source code. Notably, the source code listings were kept by the DOS creator himself, offering a window into the development process, including the chronological order of feature implementations. Subsequently, relevant physical artifacts will be donated to museums. This 'software archaeology' endeavor, guided by a team of experts and entailing a meticulous process, has culminated in Microsoft uploading the code to GitHub and releasing it under the MIT License. Through these projects, developers can delve into the fundamental logic and historical nuances of early operating systems.