What's the function of +5VSB
We can find +5VSB definition from the ATX power supply specification, but what's the function of +5VSB? We know, early AT power supply use a power button directly to turn on/off the computer. this button was usually soldered to the wires and could not be replaced easily. but newer ATX power supply use a logic switch from the motherboard to turn on/off the power supply.
The logic switch is realized by the +5VSB(Standby) supply. So +5VSB is used as a soft boot signal. Some features listed here.
the same level as the regular +5V
+5VSB has the same level as the regular +5V from the power supply, but the wire does not connect to the +5V. +5VSB has a dedicated design and a special definition mentioned below.
+5VSB is always on
+5VSB is always on even the computer is powered off, unless you cut off the power supply manually(the total wires, or the switch back of the power supply).
Wake up the computers at any time
+5VSB is used to supply the power control circuit when the computer is powered off, so it is not truly off completely. we can active/wake up this power on signal at any time by some ways(Mouse/Keyboard/Modem, etc). I'll introduce them in my other documents.
The ninth-pin in ATX power supply connector
+5V Standby is the ninth-pin in ATX power supply connector, the wire's color is purple.