as well as control signals such as psu ok psu on etc the 5v standby voltage is used for powering the alarm module 78 the other voltages are for powering the motherboard and other main system components the various lines could be configured using bus bars wires printed circuit or thick film conductors as appropriate firstly the two of three circuit 232 will be explained this circuit is powered by the 5v standby voltage 231 provided from each of the power supply units 74 each of the power supply units outputs a psu ok signal via a pin on its respective connector to a corresponding psu ok line 230 a 230 b and 230 c when the power supply unit is operating correctly each of these psu ok lines 230 is connected to the two of three circuit 232 this comprises three and gates 234 236 and 238 each for comparing a respective pair of the psu ok signals the outputs of the and gates are supplied to an or gate 240 if the output of this or gate is true then at least two of the power supply units 74 are operating correctly and power can be supplied to the motherboard of the computer system this can be achieved by closing the main power line 245 an output signal 242 could be supplied to a gate 244 for example a power fet to enable current to pass to the motherboard and other system components additionally or alternatively a power ok signal 246 for controlling some other form of switch mechanism not shown if alternatively the output of the or gate 242 is false then this indicates less than two of the power supply units 74 are.