Anyone who has bought a new computer in the last couple years probably has a few PCI-Express slots sitting empty. Beyond the 16x slots we now use for video cards, PCI-Express has been slow to come into the mainstream. It has always shown promise, but a lack of devices has killed its adoption.
PCI-X, the 64-bit older brother of the PCI slots we all have in our PCs has been rapidly adopted in the server workstation segment. Its promise of bandwidth has attracted the manufacturers of Fibre Channel Cards, SCSI Cards, InfiniBand etc.
Now that these two technologies have come to stay, which one is right for you? Tom's hardware puts them to the challenge, comparing bandwidth, clock speeds etc. their conclusion is that both are more than capable of offering a high bandwidth solution, but the more devices you are using, the more PCI-Express seems to shine. Anyway, good read.
Tom's Article
here.