is the serial number on the motherboard unique

[Merrill Oveson]

Is the serial number of the motherboard unique?

I need a way to uniquely identify a computer (PC) from all other computers
(PCs) in the world.

I thought about using MAC address - but what if the computer doesn't have a
network card?

Then I thought all computers must have a motherboard - so why not use the
serial number from it?

Good idea, or is there something better?