On the MDD G4 logic board, next to the PMU Reset button, there are 4 unpopulated button pads:
S2 (no label)
S3 is marked "NMI"
S4 is marked "RESET" and
S5 is marked "POWER"
Im assuming S5 (POWER) simply duplicates the power button on the front of the case. S4 im guessing S4 (RESET) resets the machine? Yes? What i don't know is what the heck is "NMI"? Any ideas?