power distribution across the 3.3, 5, and 12v rail?

[$pade]

What component in the pc system uses which power rail and how does that change when a psu has dual or even tripple 12v rail?

 

[$pade]

I think the cpu and gfx card use the 12v rail. The hard drive might also use the 12v rail. If that is the case what component uses the 3.3 and 5v rail?