RE: 5V supply in 3.3V systems

["Ingraham, Andrew" <Andrew.Ingraham@compaq.com>]

>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.