Bus (computing): Difference between revisions

Revision as of 13:26, 22 September 2016

Revision as of 05:36, 28 September 2016

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In modern systems the performance difference between the CPU and main memory has grown so great that increasing amounts of high-speed memory is built directly into the CPU, known as a [[CPU cache|cache]]. In such systems, CPUs communicate using high-performance buses that operate at speeds much greater than memory, and communicate with memory using protocols similar to those used solely for peripherals in the past. These system buses are also used to communicate with most (or all) other peripherals, through adaptors, which in turn talk to other peripherals and controllers. Such systems are architecturally more similar to [[Distributed computing|multicomputers]], communicating over a bus rather than a network. In these cases, expansion buses are entirely separate and no longer share any architecture with their host CPU (and may in fact support many different CPUs, as is the case with [[Peripheral Component Interconnect|PCI]]). What would have formerly been a system bus is now often known as a [[front-side bus]].

Given these changes, the classical terms "system", "expansion" and "peripheral" no longer have the same connotations. Other common categorization systems are based on the buses primary role, connecting devices internally or externally, PCI vs. [[SCSI]] for instance. However, many common modern bus systems can be used for both; [[SATA]] and the associated [[eSATA]] are one example of a system that would formerly be described as internal, while in certain automotive applications use the primarily external [[IEEE 1394]] in a fashion more similar to a system bus. Other examples, like [[InfiniBand]] and [[I²C]] were designed from the start to be used both internally and externally.

===Internal buses===