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You wrote, "PCI 2.2 supports 5 volt signalling, PCI 2.3 doesn't".
Actually, PCI 2.3 does. It deleted the +5v ONLY keyed add-in cards. This was a year 2002 specification change. After that change, the move was towards lower voltage and dual 3.3V/5V operation.
"Revision 2.3 makes a significant step in migrating the PCI bus from the original 5.0 volt signaling to a 3.3 volt signaling bus."
so it's not both. the actual motherboard connector does support 3.3 & 5 volt card keys (the physical connection) but it is electrically incompatible with 5 volt only cards. if the card is a universal card that supports both 5 and 3.3 volt signalling, a PCI 2.3 bus is compatible but if the card is 5 volt signalling only, it needs a PCI 2.2 bus or else it won't work at all.
here's a sound on sound article talking about how the issue effects people like me that use PCI 2.2 sound cards to make music. my sw1000xg is not something i can go without:
it would do alot of help to many people in my situation if motherboard manufacturers would make it clear what type of PCI bus a motherboard has. put the info right on the overview page. for example: "Two PCI 2.2 Conventional bus connectors" instead of "Two PCI Conventional bus connectors". i've been doing hours of research on current intel boards and the manuals don't even make clear what PCI bus version a motherboard has because on one page it may say 2.2 and on another it says 2.3. there's no clarity and it's frustrating. this is an important specification.
Looking over this PCI-SIG press release, it states that the version 2.3 PCI specification still supports 5 volt signaling:
Support for 5 volt signaling is retained in PCI v2.3 for backward compatibility with 5 volt-keyed add-in cards, but it is expected to be eliminated in future versions of this specification, making PCI v2.3 the last PCI specification with support for 5 volt signaling.
PCI-SIG was trying to curb manufacturers from making new 5 volt add in cards in preparation for the 3.3 volt PCI slot variants down the line. Hence the language about 5 volt cards being non-compliant. However when PCI Express proved to be a much better solution, the transition to PCI-X and the need for the lower power 3.3 volt PCI slots never really materialized in the consumer sector. Aside from some older Macintoshes, I haven't seen anything but the 5 volt keyed PCI slot used in desktop boards.
nails & potsdam, thank you both. you have enlightened me. i wasn't really paying close attention to the language.
" 2.3 No Longer Supports 5 Volt only Keyed Add-in Cards" doesn't mean 5 volt cards won't work in a PCI 2.3 motherboard connector, it just means that if a manufacturer wants to produce a pci 2.3 compliant card, it has to have the 3.3 volt key to be in spec. so it has to do with the card, not the actual motherboard connector and motherboard PCI signalling. for some reason, it sounded to me like the slot didn't support the 2.2 cards.
now pertaining the the motherboard slot /connector where the card plugs into:
"Support for 5 volt signaling is retained in PCI v2.3 for backward compatibility with 5 volt-keyed add-in cards, but it is expected to be eliminated in future versions of this specification, making PCI v2.3 the last PCI specification with support for 5 volt signaling."
which means, if my PCI 2.1 or 2.2 card fits in a PCI motherboard connector, it has to work. my 5 volt only signalling card won't even physically fit into a slot that is only 3.3 volt signalling. "PCI 3.0 Removed support for the 5.0 volt keyed system board connector". PCI 3.0 slot is incompatible because 5 volt only keyed/signaled card can't/wont fit.
so according to this knowledge, all the new MOBO models i specified in my original post do support cards that are 5 volt keyed only and 5 volt signalling only. a PCI 2.1 or 2.2 card will function properly in a PCI 2.3 motherboard slot.
for those on the net pulling their hair out, the SW1000XG PCI 2.1 card will work in a PCI 2.3 motherboard connector slot for the reasons mentioned above. if the SW1000XG fits into a PCI slot, it is both physically (the key) and electrically (signalling) compatible.
P.S, the only question left is why those intel manuals initially say those motherboards i mentioned are PCI 2.2 on one page and then PCI 2.3 on another?