PCI-Express Slots

In the picture above, the PCI Express slots (from top to bottom: x4, x16, x1 and x16), compared to a traditional 5-volt 32-bit PCI slot (bottom). As is immediately clear, traditional PCI boards (whether 3.3 volt, 5 volt, or universal) will not even fit into a PCI Express slot.

PCI Express has several shorthand names, including: PCIe, PCI-E, PCX. Note that PCI Express should not be confused with PCI-X, which is simply a different animal.

Below is a PCI-Express board, showing the edge connector. This is an x4 board. It can be installed in either an x4 or an x16 slot: