Abstract: In a computer system, which comprises a plurality of system components, typically in the form of circuit card units, and a common power bus for interconnecting the circuit card units, there are provided a main power supply, an auxiliary power supply and control switches on the power-supplying rails for selectively activating and deactivating circuit elements on the system components (in the form of circuit cards) so that as cards are added or removed, the power can be carefully controlled. According to an insertion method of the invention, undesired disruption of power is prevented by proper sequential deactivation and activation of the power lines from the main power supply and the auxiliary power supply, both of which are for providing power to multiple card units simultaneously. A live removal method also prevents undesired power disturbances.