Introduction: A Mac is a PC
True statement: Macs actually are PCs. The term PC is an abbreviation for personal computer, and a Mac is, in its own right, a personal computer. So, why do we not refer to Macs as PCs? The simple answer is: Macs are so thoroughly branded and different from other PCs that people refer to them as Macs. A Mac is like a BMW and a PC is like a nice fully restored Chevy Camaro. They are different, but they are both cars.
If you take apart a Mac computer, and you take apart a PC, you will find that they use the same parts and components. Both have: a motherboard, processor, RAM memory, graphics card, optical drive, hard drive, heatsink, fan, etc... They use the same basic hardware. The Mac BMW and the PC Camaro both have an engine, exhaust, intake, wheels, etc...
However, they do not use the same software... which brings us to difference #1.