it doesnt. 32-bit processors can ONLY address 4GB. And thats the full address map end to end.

Macs, and any computer in general has addressing for ROM, peripherals, interrupts, and other stuff.

4GB is assuming its all RAM from end to end, which isnt possible for obvious reasons, you would have no memory mapped I/O! Newer CPUs have physical address extensions that can handle more than 4GB of addressing but I have no idea how that works, other than the fact that it extends addressing above 32 bit.