“Hello, I’m a Mac…but I’m also a PC.”
The use of the terms PC and Mac to differentiate computers that run the Microsoft Windows operating system between those that run Apple OS X is technically incorrect. A few years back, Mac was simply an abbreviation for Macintosh (the brand of computers made by Apple Inc.) and PC was an acronym for Personal Computer (those used in the home/office, etc.). Recently, however, these words have changed their connotations and this transformation hasn’t been accidental.
Before I speculate how or why, let’s cover some basics. Both and Microsoft and Apple Inc. are software/hardware companies:
Microsoft develops the popular operating system “Windows” but they don’t actually manufacture the computers that it runs on. They leave it up to other companies such as Lenovo, HP, Dell, Gateway and even Apple (after the transition from the PowerPC line of processors to the Intel chip) to make hardware that is compatible with their OS. Then these individual companies give their computers their own names (i.e. the HP Pavillion or the Gateway LT Series). So for example, as a consumer you can own a Dell Inspiron that runs Microsoft Windows (God forbid that actually be the case).
On the other hand, Apple develops the “X” operating system (OS X)* and manufactures the computers that run it. Furthermore (and unlike Microsoft) Apple doesn’t allow other companies to make computers that run their “ground-breaking” operating system — Apple handles it all. So as a consumer, you can’t for example, own an HP Pavillion that runs Apple OS X. If you want Apple’s OS you need to go get an Apple computer (which has a brand name of “Mac”).
In this regard, Apple is a monopoly; the control of their hardware and of the operating system that allows users to interact with it is very stringent. So in this case, there’s no need to identify both the kind of computer you have and which operating system it runs. The entire package is simply referred to as “a Mac.” This inseparable unification of hardware and software that Apple maintains is what I think has made a “Mac” represent much more than simply a brand name.
At the same time, Apple has made efforts to practically abandoned “PC” as a label for anything about them by inaccurately using the label “PC” as an umbrella phrase to encompass everything that is not a Mac (specifically referring to computers that run Windows).