The PCI express link design of the Trenton BPG4 backplane supports PICMG 1.3 graphics 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 slot PCIe3 is a x16 mechanical slot connected directly to the SHB and driven with a x16 PCIe electrical link. 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 a Trenton SHB.