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RE: 5V supply in 3.3V systems
>What does the spec say about the 5V supply in 3.3V systems? Will the 5V
>supply always be there, even on a 3.3V only PCI motherboard?
According to the spec, the 5V supply voltage must always be provided:
"All PCI connectors require four power rails: +5V, +3.3V, +12V, and -12V.
Systems that provide PCI connectors are required to provide all four power
rails in every system ..."
+3.3V was missing from some motherboards because of an exception that
applied only to the +3.3V supply, only on motherboards with 5V PCI
connectors, and only before about 1998.