PCI Express backplane with a single expansion slot. The OSS target backplane supports a PCIe Gen3 target cable adapter installed in the OSS target slot and one or more PCIe x16 expansion cards installed in the expansion slots. Slots are backward compatible and support Gen 1 and Gen 2 target adapters and expansion cards. Only target adapters with the OSS target slot configuration are supported. Expansion cards designed to the PCIe PCI-SIG specification are supported. While the backplane is used in the CUBE products, it can also be used in test applications as a stand-alone backplane with 12VDC power applied.