On July 27, 1981, Gates fully licensed the "quick and dirty operating system" (QDOS) from a company called Seattle Computer Systems, according to The Register. That OS would later become known as MS-DOS.
Not that long before this historical purchase, IBM came a'knockin' at Microsoft's door, in search of a 16-bit OS to run on its early PCs. Microsoft apparently thought it wiser to buy an existing solution than to build its own, so at first it non-exclusively licensed what was then called 86-DOS, or QDOS, from Seattle Computer Systems. Shortly thereafter, on July 27, Microsoft dropped another $50,000 for the exclusive rights.
In about a month's time, the software shipped on an IBM PC, according to Gizmodo. Later, MS-DOS became a legendary early OS. Microsoft and IBM started cozying up to each other in a relationship that would span decades and shape the tech world. Gates (and Cofounder Paul Allen and lots of other Microsofters) got very rich.
The rest is history.
Get the Windows Central Newsletter
All the latest news, reviews, and guides for Windows and Xbox diehards.
Al Sacco is content director of Future PLC's Mobile Technology Vertical, which includes AndroidCentral.com, iMore.com and WindowsCentral.com. He is a veteran reporter, writer, reviewer and editor who has professionally covered and evaluated IT and mobile technology, and countless associated gadgets and accessories, for more than a decade. You can keep up with Al on Twitter and Instagram.