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Backbone This is computer jargon given to the physical computer network, and is usually used in reference to ethernet networks. All computers attached to the network are described as nodes. See Ethernet.

Bandwidth The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second (bps) or more commonly Mbps. This is also known as transfer rate.

Big endian Words in computers, are created from 2 or 4 bytes. In a big-endian architecture, the leftmost byte of a word is the most significant. In a little-endian architecture, the rightmost byte is most significant. Most PCs use little endian architecture; big endian architecture is mainly used in larger computers. See Little endian, Word and byte.

BIR See British Institute of Radiology.

bit The smallest unit of data storage on a computer. The word comes from binary digit; a bit can hold exactly one of two values 0 or 1. However to hold meaningful information it is necessary to combine bits into larger units known as bytes. See byte.

bits per second (bps) A measure of the transfer rate that data travels over networks. It is usually expressed in Megabits per second, or Mbps. See bit.

bps See bits per second.

Bridge A device that connects two local-area networks (LANs), or two segments of the same LAN. The two LANs being connected can be alike or dissimilar, i.e. they may follow different protocols. Unlike routers, bridges are protocol independent. They simply forward packets (blocks of data) without analysing and re-routing messages. Consequently, they are faster than routers, but also less versatile. See Hub, Router and Switch.

Brightness An attribute of a visual sensation where an area appears to emit more or less light. Brightness is perceived by an observer when photons fall on the rods and cones of the eye's retina, and is not a measurable quantity. Luminance is the measured quantity which closely corresponds to brightness and is measured in candela per square metre. In PACS, it usually refers to the brightness of a display monitor.

British Institute of Radiology (BIR) British based society with an interest in the promotion and study of radiology ( http://www.bir.org.uk/ ). See American College of Radiology (ACR) and Radiological Society of North America (RSNA).

British Standards Institute (BSI) This agency creates standards for all equipment and goods sold in the UK. The BSI also acts as a testing and inspection body for 'fitness for purpose' and safety for goods and commodities ( http://www.bsi-global.com/index.html ). See American National Standards Institute (ANSI).

Browser See Web browser.

BSI See British Standards Institute.

byte The abbreviation for binary term, the smallest unit of storage capable of representing a single character. On all modern computers, a byte comprises 8 bits. See bit.