spot on. here's the more detailed version:
expansions cards (pci and agp at any rate) have notches along the connector as a mechanism to stop them being plugged into the wrong hole.
for example, a PCI 2.2 slot looks like this (front of case to the left):
a PCI-X slot looks like this:Code:[ | ]
a card with a notch at the back can fit into a PCI slot, but not PCI-X - because of the sticky out bit at the front of a PCI-X slot. a card with a notch at the front can fit into a PCI-X slot but not a PCI slot - because of the sticky out bit at the back of the connector.Code:[ | | ]
most PCI cards have notches in both places, to work in both slots:
http://3dfusion.de/artikel/sb_xfi_xt.../xfi_karte.jpg
PCI-X cards with both notches will work in regular PCI, even though the rear set of connectors will hang out:
http://highpoint-tech.com/image/prod...0_card_big.jpg
PCI-X cards with only a front notch are designed to not work in regular PCI slots:
http://www.starline.de/bilder/produk..._mr_s3008X.jpg
if your PCI cards have only rear notches, then they won't work in PCI-X slots. but this is incredibly uncommon.