XIO


XIO is a packet-based, high-performance computer bus employed by the SGI Origin 2000, Octane, Altix, Fuel and Tezro machines. The XIO forms a bus between high-performance system devices and the memory controller.
XIO is usually used in a star topology, using a router ASIC called Crossbow to connect up to eight fully symmetrical devices in a system. Other devices known to have XIO interfaces are:
The XIO employs two source-synchronous channels, each 8 or 16 bits wide. They are clocked at 400 MHz to achieve peak rates of 800 MB/s. Each of the devices can utilize the full bandwidth, as the XBow router prevents collisions by being able to route between any two points.
Transfer is organized into micropackets. These contain a total of 128 bits of data and 32 bits of control. The control information encapsulates an 8 bit sideband, sequence numbers and check bits.
It is probable that XIO uses STL low-voltage single-ended I/O standard. CrossTown is a version of XIO utilizing PECL for differential I/O standard for longer connections.
Higher-level encapsulation differs from NUMAlink. It is well suited for short memory transactions.
XIO uses very delicate compression connectors, which should be handled with extreme care.