PCI Express is a recent addition to many new motherboards. PCI-E is replacing PCI which is currently going down in production along with AGP which is nearly extent. PCI-E offers a greater bandwidth than that of PCI and AGP. It is also structured different in that PCI used Bus and PCI-E uses serial point-to-point links called lanes.

Interface	Bandwidth [Transmit Both ways]
PCI	132 MB/s
AGP 8X	2,100 MB/s
PCI Express 1x	250 [500]* MB/s
PCI Express 2x	500 [1000]* MB/s
PCI Express 4x	1000 [2000]* MB/s
PCI Express 8x	2000 [4000]* MB/s
PCI Express 16x	4000 [8000]* MB/s
PCI Express 32x	8000 [16000]* MB/s