Skip to main content

concurrency

concurrency The progressing of two or more activities (processes, programs) in parallel. It is a term that describes the general topic of parallelism in computer systems, specifically multiprocessing systems. Specification of concurrency, and the consequent problems of interlock and synchronization, requires special features in the programming language, and is a feature of the class of real-time languages.

The usual method of describing parallelism is Flynn's classification, which does so in terms of parallelism in the instruction stream and in the data stream of a system. Thus there are four categories:

SISD, single instruction, single data;

SIMD, single instruction, multiple data;

MISD, multiple instruction, single data;

MIMD, multiple instruction, multiple data.

The first of these, SISD, is the conventional serial processor. The third of these, MISD, does not really occur in current systems. The other two are of most interest in multiprocessor systems. The SIMD is suited to operating upon data of the sort that exists in vectors and matrices by taking advantage of the inherent parallelism in that data. Thus the array processor is one such system. Another is represented by the supercomputer with parallel and different arithmetic units that overlap arithmetic operations. The MIMD system represents a wide range of architectures from the large symmetrical multiprocessor system to the small asymmetrical minicomputer/DMA channel combination.

Shared-memory systems form a distinct group within the MIMD category. They are general-purpose multiprocessor systems that share common memory, and are thus also called closely coupled or tightly coupled systems. Distributed systemswide area, metropolitan area, and local area networks – form another MIMD group, sometimes referred to as loosely coupled systems.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"concurrency." A Dictionary of Computing. . Encyclopedia.com. 12 Dec. 2018 <https://www.encyclopedia.com>.

"concurrency." A Dictionary of Computing. . Encyclopedia.com. (December 12, 2018). https://www.encyclopedia.com/computing/dictionaries-thesauruses-pictures-and-press-releases/concurrency

"concurrency." A Dictionary of Computing. . Retrieved December 12, 2018 from Encyclopedia.com: https://www.encyclopedia.com/computing/dictionaries-thesauruses-pictures-and-press-releases/concurrency

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.