There is a long article on OS/2 in Ars Technica
https://arstechnica.com/information-technology/2019/11/half-an-operating-system-the-triumph-and-tragedy-of-os2/It was a cloudy Seattle day in late 1980, and Bill Gates, the young chairman of a tiny company called Microsoft, had an appointment with IBM that would shape the destiny of the industry for decades to come.
He went into a room full of IBM lawyers, all dressed in immaculately tailored suits. Bill’s suit was rumpled and ill-fitting, but it didn’t matter. He wasn’t here to win a fashion competition.
Over the course of the day, a contract was worked out whereby IBM would purchase, for a one-time fee of about $80,000, perpetual rights to Gates’ MS-DOS operating system for its upcoming PC. IBM also licensed Microsoft’s BASIC programming language, all that company's other languages, and several of its fledging applications. The smart move would have been for Gates to insist on a royalty so that his company would make a small amount of money for every PC that IBM sold.
But Gates wasn’t smart. He was smarter.
In exchange for giving up perpetual royalties on MS-DOS, which would be called IBM PC-DOS, Gates insisted on retaining the rights to sell DOS to other companies. The lawyers looked at each other and smiled. Other companies? Who were they going to be? IBM was the only company making the PC. Other personal computers of the day either came with their own built-in operating system or licensed Digital Research’s CP/M, which was the established standard at the time.
Gates wasn’t thinking of the present, though. “The lesson of the computer industry, in mainframes, was that over time people built compatible machines,” Gates explained in an interview for the 1996 PBS documentary Triumph of the Nerds. As the leading manufacturer of mainframes, IBM experienced this phenomenon, but the company was always able to stay ahead of the pack by releasing new machines and relying on the power of its marketing and sales force to relegate the cloners to also-ran status.
The personal computer market, however, ended up working a little differently. PC Cloners were smaller, faster, and hungrier companies than their mainframe counterparts. They didn’t need as much startup capital to start building their own machines, especially after Phoenix and other companies did legal, clean-room, reverse-engineered implementations of the BIOS (Basic Input/Output System) that was the only proprietary chip in the IBM PC’s architecture. To make a PC clone, all you needed to do was put a Phoenix BIOS chip into your own motherboard design, design and manufacture a case, buy a power supply, keyboard, and floppy drive, and license an operating system. And Bill Gates was ready and willing to license you that operating system.
https://arstechnica.com/information-technology/2019/11/half-an-operating-system-the-triumph-and-tragedy-of-os2/[follow the link for the rest of the story]