XIO is a packet-based, high-performance

computer bus In computer architecture, a bus (historically also called a data highway or databus) is a communication system that transfers data between components inside a computer or between computers. It encompasses both hardware (e.g., wires, optical ...

employed by the

SGI Origin 2000 The SGI Origin 2000 is a family of mid-range and high-end server computers developed and manufactured by Silicon Graphics (SGI). They were introduced in 1996 to succeed the SGI Challenge and POWER Challenge. At the time of introduction, these ...

Octane Octane is a hydrocarbon and also an alkane with the chemical formula C8H18, and the condensed structural formula CH3(CH2)6CH3. Octane has many structural isomers that differ by the location of branching in the carbon chain. One of these isomers ...

Altix Altix is a line of server computers and supercomputers produced by Silicon Graphics (and successor company Silicon Graphics International), based on Intel processors. It succeeded the MIPS/IRIX-based Origin 3000 servers. History The line was ...

Fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work (physics), work. The concept was originally applied solely to those materials capable of releasing chem ...

and Tezro machines. The XIO forms a bus between high-performance system devices and the

memory controller A memory controller, also known as memory chip controller (MCC) or a memory controller unit (MCU), is a digital circuit that manages the flow of data going to and from a computer's main memory. When a memory controller is integrated into anothe ...

. XIO is usually used in a star topology, using a router

ASIC An application-specific integrated circuit (ASIC ) is an integrated circuit (IC) chip customized for a particular use, rather than intended for general-purpose use, such as a chip designed to run in a digital voice recorder or a high-efficien ...

called Crossbow (Xbow) to connect up to eight fully symmetrical devices in a system (one of them is usually the memory controller /

CPU A central processing unit (CPU), also called a central processor, main processor, or just processor, is the primary processor in a given computer. Its electronic circuitry executes instructions of a computer program, such as arithmetic, log ...

bridge, called HEART in Octane or Hub in Origin). Other devices known to have XIO interfaces are: * BRIDGE: XIO to PCI-64 bridge (Octane, Origin) * XBRIDGE: XIO to PCI-X bridge (Altix) * HQ4: command processor of ImpactSR cards (Octane) * KTOWN: frontend for InfiniteReality2 cards (Onyx, Origin variation) * XC: Crosstown converter * BUZZ: "OpenGL-on-a-Chip" ASIC used in ODYSSEY/VPro graphics (V6/V8/V10/V12) The XIO employs two

source-synchronous Source-Synchronous clocking refers to a technique used for timing symbols on a digital interface. Specifically, it refers to the technique of having the transmitting device send a clock signal along with the data signals. The timing of the unidire ...

channels (one in each direction), each 8 or 16 bits wide. They are clocked at 400 MHz to achieve peak rates of 800 MB/s (i.e. in megabytes). 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 (used by higher layers for framing), sequence numbers (for go-back-n link-layer retransmissions) and check bits ( CRC-16). It is probable that XIO uses STL (which SGI likes to call ''SGI transistor logic'') low-voltage single-ended I/O standard. CrossTown is a version of XIO utilizing PECL for differential I/O standard (like

NUMAlink NUMAlink is a system interconnect developed by Silicon Graphics (SGI) for use in its distributed shared memory ccNUMA computer systems. NUMAlink was originally developed by SGI for their Origin 2000 and Onyx2 systems. At the time of these system ...

) for longer connections. Higher-level encapsulation differs from NUMAlink (like used to connect HUB chips in Origin-series machines). It is well suited for short memory transactions. XIO uses very delicate compression connectors, which should be handled with extreme care.

References

{{DEFAULTSORT:Xio Computer buses