Hahaha, I wrote a paper on the early history of M$ and the Gary Killdall story, where Gates bought QDOS (the quick and dirty operating system) to offer to IBM, after sending IBM to Killdall (so IBM can get CP/M from Killdall) but after IBM came back to Gates empty-handed (cuz Killdall was out having fun, missing the opportunity of a lifetime) Gates offered that Microsoft could do the OS for IBM so M$ bought QDOS, did some changes in branding (and other tweaks) and then got it packaged for IBM’s new computers. If I recall correctly, Killdall threatened to sue, and afterwards, there was a CP/M version offered alongside the MS-DOS version. However, the MSDOS version was like $10-$20 while CP/M was in the hundreds of dollars on top of the computer itself. So Microsoft won.
BUT this was NOT the beginning of M$. They started with BASIC interpreters for Altair when Gates and Allen were at Harvard.