The IBM PC, in its original form was built from off the shelf parts. The only proprietary "component" was the BIOS. It would not have been possible to protect the PC hardware with patents. Anyone could have imitated the hardware but without the BIOS it would have been a box of wired bits.
The clean room reverse engineering* of the BIOS allowed compatibles that followed the IBM design and software function to be built.
*One engineer analyses the hardware functions of the BIOS chip
*Said engineer writes a specification
*Same engineer leaves the project - No further contact with him/her is allowed.
New engineer reads the specification and writes a program against the specification. The engienner has no sight of the BIOS chip or its operation. His/her code is original.
This code was to all intents and purposes functionally identical to the IBM BIOS. (These days a patent breach) The copy BIOS contained no IBM code, copyright remains in tact.
In turn, this meant that Microsoft only needed to make one version of DOS instead of the vatiations that were being planned / produced for the "nearly compatible" computers that were in the pipeline.
A standard PC clone was born and the rest is history...