From LXF Wiki
PC is an initialism for Personal Computer, and in its proper use, could equally refer to an Apple Mac, Atari ST, Amiga, Archimedes or even a PDA. However, it has come to be used almost exclusively in relation to x86 architecture computers, mainly because these processors were popularised by the hugely successful IBM PC specification.
IBM were the first manufacturer to publicly release the design specification of their Personal Computer and allow clones to be built. This was an early example of "open sourcing" (though it was not truly free in the modern sense, because IBM retained control of the source for some years, and various companies still own proprietary IP rights). The move was hugely popular, kickstarting the near-monopoply enjoyed ever since by the x86-based architecture. Sadly for IBM, the clone-makers soon cut their PC business from under them, and IBM took a while to get their act back together.
A side effect of all this was Microsoft's monopoly hold on the IP necessary to write an Operating system for the PC architecture.