Editing Symmetric multiprocessing (section)

== Alternatives ==

[[Image:Shared memory.svg|right|350px|thumb|Diagram of a typical SMP system. Three processors are connected to the same memory module through a [[system bus]] or [[crossbar switch]]. ]]

SMP uses a single shared [[system bus]] that represents one of the earliest styles of multiprocessor machine architectures, typically used for building smaller computers with up to 8 processors.

Larger computer systems might use newer architectures such as [[Non-Uniform Memory Access|NUMA]] (Non-Uniform Memory Access), which dedicates different memory banks to different processors.  In a NUMA architecture, processors may access local memory quickly and remote memory more slowly.  This can dramatically improve memory throughput as long as the data are localized to specific processes (and thus processors). On the downside, NUMA makes the cost of moving data from one processor to another, as in workload balancing, more expensive. The benefits of NUMA are limited to particular workloads, notably on [[Server (computing)|server]]s where the data are often associated strongly with certain tasks or users.

Finally, there is [[computer cluster]]ed multiprocessing (such as [[Beowulf (computing)|Beowulf]]), in which not all memory is available to all processors. Clustering techniques are used fairly extensively to build very large supercomputers.