Microsoft's operating system business launched 30 years ago today with MS-DOS ... kind of. As The Register reports, on July 27, 1981 Microsoft bought the full rights to QDOS (Quick and Dirty Operating System), the PC operating system the company acquired from Seattle Computer Products. Microsoft also renamed the OS that day to MS-DOS. The price that Microsoft paid Seattle Computer Products for QDOS? A mere $50,000. (It had previously licensed the operating system from Seattle Computer Products for $25,000).
SCP still retained the rights to use the operating system with its own PCs. However Microsoft started making its massive amounts of money when it licensed MS-DOS to IBM for its PC. Launched in August 1981, the IBM PC eventually became the basis for nearly all personal computers and as a result Microsoft's operating system was installed on nearly every one of those PCs.
Microsoft continued to develop MS-DOS with a number of different versions over the years and while there were competitors that released their own DOS-based operating systems none of them seriously competed with Microsoft's OS. Even as it launched its graphical Windows operating system in 1985, MS-DOS was still supported and updated by Microsoft as some developers continued to use the OS for its programs, particularly for PC gaming. With the release of Windows 95 in 1995 gaming programmers finally moved over completely to the Windows operating system. The last stand alone retail version of MS-DOS was version 6.22 released in 1994. Version 7 and 8 of MS-DOS were released as part of Windows 95 and Windows Me, respectively.