In November 1980, Microsoft signed an agreement with to provide an operating system for the still-secret IBM Personal Computer, to be released in 1981. The operating system would ultimately be called PC-DOS, a .

Microsoft didn't actually write MS-DOS; instead it paid to have Seattle Computer rewrite its own QDOS (Quick-and-Dirty Operating System) for the purpose, without telling Seattle Computer to whom the operating system would be sold. (Microsoft signed the contract with Seattle Computer one day after signing the contract with IBM.)

QDOS was largely based on the , owned by Digital Research. Ironically, IBM had originally turned to Digital Research for an operating system for the IBM PC, but the two companies' negotiations broke down. Too bad for Digital Research; Microsoft went on to use its relationship with IBM as a springboard to develop its worldwide dominance in business operating systems.

In July 1987, . for $14 million in cash. Forethought had developed a presentation program for the Macintosh, initially called Presenter, which it renamed PowerPoint for trademark reasons. PowerPoint later became one of the core programs of , which for many years has been the dominant office productivity suite.