PCI Express

PCI Express (PCIe) adapters use a different type of slot than Peripheral Component Interconnect (PCI) and Peripheral Component Interconnect-X (PCI-X) adapters. If you attempt to force an adapter into the wrong type of slot, you might damage the adapter or the slot. A PCI adapter can be installed in a PCI-X slot, and a PCI-X adapter can be installed in a PCI adapter slot. A PCIe adapter cannot be installed in a PCI or PCI-X adapter slot, and a PCI or PCI-X adapter cannot be installed in a PCIe slot. The following illustration shows an example of a PCI-X adapter (A) next to a PCIe 4x (B) adapter.

PCIe adapters and slots come in 4 different sizes: 1x, 4x, 8x, and 16x. Smaller size adapters do fit in larger slots, but larger size adapters do not fit in smaller slots. Table 1 shows PCIe slot compatibility.