InfiniBand is a type of communications link for data flow between processors and I/O devices that offers throughput of up to 2.5 gigabytes per second and support for up to 64,000 addressable devices. Because it is also scalable and supports quality of service (QoS) and failover, InfiniBand is often used as a server connect in high-performance computing (HPC) environments.The internal data flow system in most PCs and server systems is inflexible and relatively slow. As the amount of data coming into and flowing between components in the computer increases, the existing bus system becomes a bottleneck. Instead of sending data in parallel (typically 32 bits at a time, but in some computers 64 bits) across the backplanebus, InfiniBand specifies a serial (bit-at-a-time) bus. Fewer pins and other electrical connections are required, saving manufacturing cost and improving reliability. The serial bus can carry multiple channels of data at the same time in a multiplexing signal. InfiniBand also supports multiple memory areas, each of which can addressed by both processors and storage devices.The InfiniBand Trade Association views the bus itself as a switch because control information determines the route a given message follows in getting to its destination address. InfiniBand uses Internet Protocol Version 6 (IPv6), which enables an almost limitless amount of device expansion.With InfiniBand, data is transmitted in packets that together form a communication called a message. A message can be a remote direct memory access (RDMA) read or write operation, a channel send or receive message, a reversible transaction-based operation or a multicast transmission. Like the channel model many mainframe users are familiar with, all transmission begins or ends with a channel adapter. Each processor (your PC or a data center server, for example) has what is called a host channel adapter (HCA) and each peripheral device has a target channel adapter (TCA). These adapters can potentially exchange information that ensures security or work with a given Quality of Service level.The InfiniBand specification was developed by merging two competing designs, Future I/O, developed by Compaq, IBM, and Hewlett-Packard, with Next Generation I/O, developed by Intel, Microsoft, and Sun Microsystems.