In computer parlance, a data bus—also called a processor bus, front side bus, frontside bus or backside bus—is a group of electrical wires that sends information (data) between two or more components. The Intel processor in the current line of Macs, for example, uses a 64-bit data bus to connect the processor to its memory.
Bus Width
A data bus has many different defining characteristics, but one of the most important is its width. The width of a data bus refers to the number of bits (electrical wires) that make up the bus. Common data bus widths include 1-, 4-, 8-, 16-, 32-, and 64-bit.
When manufacturers refer to the number of bits a processor uses, such as “This computer uses a 64-bit processor,” they are referring to the width of the front side data bus, the bus that connects the processor to its main memory. Other types of data buses used in computers include the backside bus, which connects the processor to the dedicated cache memory.
A data bus is typically governed by a bus controller that regulates the speed of information between components. Generally, everything needs to travel at the same speed within a computer and nothing can travel faster than the CPU. Bus controllers keep things moving at the same speed.
Early Macs used a 16-bit data bus; the original Macintosh used a Motorola 68000 processor. Newer Macs use 64-bit buses.
Types of Buses
A data bus can operate as a serial or a parallel bus. Serial buses—like USB and FireWire connections—use a single wire to both send and receive information between components. Parallel buses—like SCSI connections—use many wires to communicate between components. Those buses may be internal to the processor or external, relative to a given component being connected.
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