Where is the 'identity' of the Wii stored?

I have a spare Wii that's almost never been used, and was thinking of swapping my mom's Wii into it, rather than just swapping out the DVD drive which has gone south.

But what part is it that stores the 'identity' of the machine (eg, settings, saved games, etc.)

I was planning on swapping the motherboard, but thought I'd ask first if anyone else has tried it, to see if there's something else I might need to move as well, or if there's something on the motherboard that could be disconnected and moved.