System Host Board PCI Express Specification
The SHB Express SHBs are defined in two form factors: full-size and half-size SHB’s. The full-size SHB length is identical to the ISA long board length and height. Half-size SHB form factor is based on the half-size PCIe and PCI board in length, while following the ISA board height. The SHB Express™ SHB is designed to interface with PCI Express peripherals on a backplane. The PCI Express interconnects with the backplane can operate at x1, x4, x8, x16, and others depending on the capabilities of both the SHB and the backplane.