Basically the title
IBM built the original PC from off the shelf components and for some reason negotiated a non-exclusive license for MS-DOS with Microsoft. The only thing in the PC they held a copyright on was the BIOS ROM. A few companies tried making clones, IIRC Eagle Computer just brazenly dumped the IBM BIOS and used that and got sued out of existence. I believe it was Compaq that developed their own MS-DOS compatible BIOS from scratch that did not infringe so IBM had no case to sue. IBM got a competitor they didn’t want, and the PC became a 40 year platform.
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