"Each GPC power on , off switch is a guarded switch. Positioning a switch to on provides the computer with triply redundant
power (not through a discrete) by three essential buses-ESS1BC, 2AC and 3AB-which run through the GPC power switch. The
essential bus power is transferred to remote power controllers, which permits main bus power from the three main buses (MNA,
MNB and MNC) to power the GPC. There are three RPCs for the IOP and three for the CPU; thus, any GPC will function
normally, even if two main or essential buses are lost. "
Acknowledgement: NASA Shuttle Reference Pages
