The oldest-known version of MS-DOS’s predecessor has been discovered and uploaded

Enlarge / The IBM PC 5150. (credit: SSPL/Getty Images)

Microsoft’s MS-DOS (and its IBM-branded counterpart, PC DOS) eventually became software juggernauts, powering the vast majority of PCs throughout the ’80s and serving as the underpinnings of Windows throughout the ’90s.

But the software had humble beginnings, as we’ve detailed in our history of the IBM PC and elsewhere. It began in mid-1980 as QDOS, or “Quick and Dirty Operating System,” the work of developer Tim Paterson at a company called Seattle Computer Products (SCP). It was later renamed 86-DOS, after the Intel 8086 processor, and this was the version that Microsoft licensed and eventually purchased.

Last week, Internet Archive user f15sim discovered and uploaded a new-old version of 86-DOS to the Internet Archive. Version 0.1-C of 86-DOS is available for download here and can be run using the SIMH emulator; before this, the earliest extant version of 86-DOS was version 0.34, also uploaded by f15sim.