In 1979 Gates and Allen moved the company to Bellevue, Washington, a suburb of their hometown of Seattle. (The company moved to its current headquarters in Redmond in 1986.) In 1980 International Business Machines Corporation (IBM) chose Microsoft to write the operating system for the IBM PC personal computer, to be introduced the following year. Under time pressure, Microsoft purchased 86-DOS (developed by programmer Tim Paterson and originally called QDOS for Quick and Dirty Operating System) from a small company called Seattle Computer Products for $50,000, modified it, and renamed it MS-DOS (Microsoft Disk Operating System).
As part of its contract with IBM, Microsoft was permitted to license the operating system to other companies. By 1984 Microsoft had licensed MS-DOS to 200 personal computer manufacturers, making MS-DOS the standard operating system for PCs and driving Microsoft’s enormous growth in the 1980s. Allen left the company in 1983 but remained on its board of directors until 2000. Allen continues to be a major shareholder in Microsoft.