Multiprocessing is the coordinated processing of programs by more than one computer processor. Multiprocessing is a general term that can mean the dynamic assignment of a program to one of two or more computers working in tandem or can involve multiple computers working on the same program at the same time (in parallel).

With the advent of parallel processing, multiprocessing is divided into symmetric multiprocessing (SMP) and massively parallel processing (MPP).

In symmetric (or "tightly coupled") multiprocessing, the processors share memory and the I/O bus or data path. A single copy of the operating system is in charge of all the processors. SMP, also known as a "shared everything" system, does not usually exceed 16 processors.

In massively parallel (or "loosely coupled") processing, up to 200 or more processors can work on the same application. Each processor has its own operating system and memory, but an "interconnect" arrangement of data paths allows messages to be sent between processors. Typically, the setup for MPP is more complicated, requiring thought about how to partition a common database among processors and how to assign work among the processors. An MPP system is also known as a "shared nothing" system.

Multiprocessing should not be confused with multiprogramming, or the interleaved execution of two or more programs by a processor. Today, the term is rarely used since all but the most specialized computer operating systems support multiprogramming. Multiprocessing can also be confused with multitasking, the management of programs and the system services they request as tasks that can be interleaved, and with multithreading, the management of multiple execution paths through the computer or of multiple users sharing the same copy of a program.

This was last updated in September 2005

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