Two of the PCIe card slots on the PCI Express backplane are driven with interface links direct from the SBC. The remaining four x8 PCIe slots available on the backplane are driven with x4 links from a 24-lane PCI Express switch. The PCIe switch also provides a x4 link that drives the dual-channel PCIe-to-PCI-X bridge which interfaces the PCI-X/PCI option card slots to the SBC.