It is the difference between a specific proper pronoun and a generic pronoun. Mac is the nickname for the Macintosh computer made by Apple. PC is an acronym that comes from the terms personal computer. Only the Macintosh is a Mac. The Macintosh is also a PC.
Both the PC and the Mac are very good for their own reasons. Here is a list of the main advantages of each:
Advantages of a PC
- Much more popular, over 80% of all desktop computers use Windows
- Uses a Start Menu and taskbar at the bottom (by default)
- Easier for an inexperienced user
- Considerably cheaper
- Compatibility/Availability (most applications are developed for Windows only)
- Plays commercial games
- More customizable, hardware can be upgraded very easily.
Advantages of a Mac
- Looks much better
- Uses a Dock and a bar at the top (by default)
- Safer (almost zero viruses)
- Simpler, more reliable (less configuration, less processes)
- Macs are made by Apple themselves (not many are custom-made)
- Much more productive (Audio, Video and Image editing software is much better)
- You can install Windows easily, alongside OS X (dual-booting).