Nahh, Gates licensed DOS.
Gates shared plenty of ideas with IBM and even told them he’d write an operating system for them. Instead of writing one, Gates reached out to Paterson and purchased 86-DOS from him, allegedly for $50,000. Microsoft turned it into Microsoft Disk Operating System, or MS-DOS, which they introduced on this day in 1981.Jul 27, 2011
A Quick Look At The 30-Year History Of MS DOS - Business Insider...
https://www.businessinsider.com/history-of-dos-2011-7#ibm-approached-a-young-bill-gates-for-help-3
Gates did steal a part of Xerox’s OS to use in Windows during a visit at IBM