All computing devices, from smartphones to supercomputers, pass data back and forth along electronic channels called "buses." The number and type of buses used strongly affect the machine's overall speed. Simple computer designs move data on a single bus; multiple buses, however, vastly improve performance. In a multiple-bus architecture, each pathway is suited to handle a particular kind of information.
Speed and Efficiency
In a single-bus architecture, all components including the central processing unit, memory and peripherals share a common bus. When many devices need the bus at the same time, this creates a state of conflict called bus contention; some wait for the bus while another has control of it. The waiting wastes time, slowing the computer down. Multiple buses permit several devices to work simultaneously, reducing time spent waiting and improving the computer's speed. Performance improvements are the main reason for having multiple buses in a computer design.
Having multiple different buses available gives you more choices for connecting devices to your computer, as hardware makers may offer the same component for more than one bus type. For example, most desktop PCs use the Serial Advanced Technology Attachment interface for internal hard drives, but many external hard drives and flash drives connect via USB. If your computer's SATA connections are all used, the USB interface lets you connect additional storage devices.
As with all of a computer's components, bus designs evolve, with new types being introduced every few years. For example, the PCI bus that supports video, network and other expansion cards predates the newer PCIe interface, and USB has undergone several major revisions. Having multiple buses that support equipment from different eras lets you keep legacy equipment such as printers and older hard drives and add newer devices as well.
A single central processing unit places heavy demands on the bus that carries memory data and peripheral traffic for hard drives, networks and printers; since the mid-2000s, however, most computers have adopted a multi-core model that require additional buses. To keep each core busy and productive, the new bus designs ferry increased amounts of information in and out of the microprocessor, keeping wait times to a minimum.
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