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Unibus Trademark A minicomputer bus structure devised by Digital and used originally in their PDP 11 series of computers. It is a single bus structure that has 56 bidirectional lines and is common to peripherals, memory, and the processor. The maximum transfer rate is one 16 bit word every 750 nanoseconds. All transfers are initiated by a master device and acknowledged by the receiving or storage device. The allocation of the role of master device is dynamic and the processor can grant control of the bus in response to a request from a peripheral.