To make it short. registered(buffered) ram uses a control (type of clock) that takes a weak line of memory and boosts it to a strong line equal with the other lines of memory so that the address lines and control lines use the same voltage and remain equal.
It also has a lot to do with the amount of amps that would be required to run the ram's control lines and address lines. Most motherboards can't support the unbuffered ram because of the amps that would be requires to operate them...as in 2 gigs of buffered(registered) ram uses about 15 watts of power while the same amount of unbuffered ram would need about 40 watts of power to operate them.
>editted<
