Exactly 36 years ago today, Microsoft Cofounder Bill Gates made one of the important purchases in the software giant's storied history.

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.