4.3 THE BUS

The CPU communicates with the other components via a bus. A bus is a set of wires that acts as a shared but common datapath to connect multiple subsystems within the system. It consists of multiple lines, allowing the parallel movement of bits. Buses are low cost but very versatile, and they make it easy to connect new devices to each other and to the system. At any one time, only one device (be it a register, the ALU, memory, or some other component) may use the bus. However, this sharing often results in a communications bottleneck. The speed of the bus is affected by its length as well as by the number of devices sharing it. Quite often, devices are divided into primary and worker categories; a primary device is one that initiates ...

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