The five-slot, 6U VME64x backplane allows more room for cabling, isolators for shock and vibration, or a fan tray below the card cage. The 7U VME64x backplane version has an extra 1U of power bugs at the bottom for higher-current applications. It conforms to the VITA 1.7 High Current specification. Both come with up to 21 slots. The five-slot, 6U VME64x starts under $400.