cal tree that requires more logic bridges and longer propagation delay times, when adding additional segments to the bus. Widest data path: VME64 (64 bit): PCI (64 bit). The width of the data path has increased to 64 bits. This size is a standard option in VME64, VME64x, VME320, PCI, Compact PCI, and PCI-X. Fastest data rate: PCI-X (133 MHz, 64 bit, 1.06 Gbyte/s). The PCI protocol is, by far, the leader in speed. With the new PCI-X specification operating at 133 MHz and 64 bit data path, speeds of up to 1.06 Gbyte/s can be achieved. Current limitations allow only two cards on this high-speed segment and only one segment can run at 133 MHz, leaving the other segments to run at 66 MHz. The fastest competitor in the VME family is VME320, licensed by Arizona Digital, which has a bus band- width of over 320 Mbyte/s and a peak speed over 500 Mbyte/s. Hot-swap capabilities: Compact PCI, PCI-X, VME64, VME64x. To hot swap means to leave the bus interface component on, or in a known state while removing or inserting a card into the system. Hot swapping or live insertion is important for customers who require systems with zero downtime. All the major protocols are adopting specifications to support hot-swap capabilities. Compact PCI and VME64 both include special mechanical configurations in the connector to make and break the ground, prebias, control, and VCC connections before the data pins touch. This allows a card to be precharged and reduces insertion transients associ- ated with noise and voltage spikes. Low cost: PCI. Devices manufactured for the PCI specification, including Compact PCI and PCI-X, are generally less expensive than VME technology. PCI devices are an inexpensive, mass-produced bus and board standard, with literally thousands of suppliers competing at low margins. If VME is used, it will have some PCI in the final product because compatibility issues force VME system designers to include PCI in their products. With over 800 companies supporting PCI and designing cards and accessories for the PCI open sp