RE: 3.3V power supply.

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

The +3.3V power supply was "always" there ... but when Revision 2.0? (2.1?)
was released, due to some industry pressure the +3.3V supply was made
optional for systems that used 5V signaling.

If it was omitted, provision had to be made for it to be added it later,
including having all the +3.3V pins already wired up and bypassed.  I doubt
there were many customers who retrofitted their boxes to add the +3.3V, but
in theory such a retrofit should be available.

Because it was optional on the motherboard, PCI plug-in cards were supposed
to generate their own +3.3V from +5V or +12V as an interim solution.  (This
further encouraged motherboard vendors to leave out the +3.3V supply.)

PCI Revision 2.2, released last year, made the +3.3V supply mandatory on the
motherboard again.