Microsoft open-sources "the earliest DOS source code discovered to date"

Microsoft has released the earliest discovered DOS source code, including 86-DOS 1.00 kernel sources and PC-DOS 1.00 development snapshots, along with documentation. The code predates the MS-DOS branding and traces back to Tim Paterson's original 86-DOS (QDOS) created for Intel 8086-based systems, later licensed by Microsoft for the IBM PC.