Книга: Programming with POSIX® Threads

1.2.4 Parallelism

1.2.4 Parallelism

Parallelism describes concurrent sequences that proceed simultaneously. In other words, software "parallelism" is the same as English "concurrency" and different from software "concurrency." Parallelism has a vaguely redeeming analogy to the English definition: It refers to things proceeding in the same direction independently (without intersection).

True parallelism can occur only on a multiprocessor system, but concurrency can occur on both uniprocessor and multiprocessor systems. Concurrency can

occur on a uniprocessor because concurrency is, essentially, the illusion of parallelism. While parallelism requires that a program be able to perform two computations at once, concurrency requires only that the programmer be able to pretend that two things can happen at once.

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