Multiprocessing

Multiprocessing (or parallel processing) refers to the simultaneous use of more than one computer or processor to solve a problem. There are many different kinds of parallel computers (or "parallel processors"). They are distinguished by the kind of interconnection between processors (known as "processing elements" or PEs) and between processors and memory. also classifies parallel (and serial) computers according to whether all processors execute the same instructions at the same time ("single instruction/multiple data" - ) or each processor executes different instructions ("multiple instruction/multiple data" - ).

The processors may either communicate in order to be able to cooperate in solving a problem or they may run completely independently, possibly under the control of another processor which distributes work to the others and collects results from them (a ""). The difficulty of cooperative problem solving is aptly demonstrated by the following dubious reasoning: If it takes one man one minute to dig a post-hole, then sixty men can dig it in one second.

Usage by Apple
The Power Macintosh 9500 was the first multiprocessor model to be marketed by Apple Computer. A version with two 180 MHz PowerPC 604e processors was released on August 7, 1996. The PowerPC G3-based Macs were only available in single-processor versions, but the Power Mac G4 was available in dual-processor configurations. The Power Mac G5 was available in dual-processor, dual-core (two processing s on one ), and quad-core (four processing cores on two separate dies). Most Intel-based Macs contain at least two cores, and may optionally contain up to 28 cores. The Apple A5, used in the iPad 2 and iPhone 4S, was Apple's first multi-core mobile processor.