The PCI express link design of the Trenton BPX5 backplane supports PICMG 1.3 server class SHBs. On this PCI express-only backplane, all of the option card slots are connected directly to the system host board ensuring maximum possible PCIe data throughput speeds. Card slots PCIe3 and PCIe4 are x16 mechanical slots that are both connected directly to the SHB and driven with x8 PCIe electrical links. PCIe1 and PCIe2 are x8 mechanical slots and PCIe2 is driven with a x4 PCIe link directly from the SHB. The PCIe1 slot is driven by a x4 electrical link delivered to the card slot via an IOB33 module installed on the SHB.