Are the CEI-520A and QPCI1553 compatible with PCI-X?
The PCI-1553 and CEI-520 use +5V PCI signaling and only work in +5V PCI slots. The CEI-520A and QPCI-1553 use universal PCI signaling voltage, and work in any PCI or PCI-X slot. Because the CEI-520A and PCI-1553 operate at 33MHz, the entire PCI bus segment connected to these boards is limited to 33MHz operation. With PCI-X 133 and faster, the bus segments contain only one slot, so there are no performance issues with other cards. PCI voltage keying prevents the installation of a PCI board into an incompatible slot.