Editing Multiprocessing (section)

{{Short description|Use of two or more central processing units (CPUs) within a single computer system}}
{{Use dmy dates|date=April 2014}}
{{refimprove|date=February 2014}}
'''Multiprocessing''' ('''MP''') is the use of two or more [[central processing unit]]s (CPUs) within a single [[computer system]].<ref name="Rajagopal1999">{{cite book |author=Raj Rajagopal |title=Introduction to Microsoft Windows NT Cluster Server: Programming and Administration |url=https://books.google.com/books?id=kUJnHJJlnpUC&pg=PA4 |year=1999 |publisher=CRC Press |isbn=978-1-4200-7548-9 |page=4}}</ref><ref name="EbbersKettner2012"/> The term also refers to the ability of a system to support more than one processor or the ability to allocate tasks between them. There are many variations on this basic theme, and the definition of multiprocessing can vary with context, mostly as a function of how CPUs are defined ([[multi-core (computing)|multiple cores]] on one [[Die (integrated circuit)|die]], multiple dies in one [[Chip carrier|package]], multiple packages in one [[system unit]], etc.).

A '''multiprocessor''' is a computer system having two or more [[Central processing unit|processing units]] (multiple processors) each sharing [[main memory]] and peripherals, in order to simultaneously process programs.<ref>{{cite web |url=http://www.yourdictionary.com/multiprocessor |title=Multiprocessor dictionary definition - multiprocessor defined |website=www.yourdictionary.com |access-date=16 March 2018 |archive-date=16 March 2018 |archive-url=https://web.archive.org/web/20180316151954/http://www.yourdictionary.com/multiprocessor |url-status=live }}</ref><ref>{{cite web |url=http://www.thefreedictionary.com/multiprocessor |title=multiprocessor |access-date=16 March 2018 |via=The Free Dictionary |archive-date=16 March 2018 |archive-url=https://web.archive.org/web/20180316151656/http://www.thefreedictionary.com/multiprocessor |url-status=live }}</ref> A 2009 textbook defined multiprocessor system similarly, but noted that the processors may share "some or all of the system’s memory and I/O facilities"; it also gave '''tightly coupled system''' as a synonymous term.<ref>{{cite book |author=Irv Englander |title=The architecture of Computer Hardware and Systems Software. An Information Technology Approach. |publisher=Wiley |date=2009 |edition=4th | isbn=978-0471715429 |page=265}}</ref>

At the [[operating system]] level, ''multiprocessing'' is sometimes used to refer to the execution of multiple concurrent [[Process (computing)|processes]] in a system, with each process running on a separate CPU or core, as opposed to a single process at any one instant.<ref name="MorleyParker2012">{{cite book |author1=Deborah Morley |author2=Charles Parker |title=Understanding Computers: Today and Tomorrow, Comprehensive |url=https://books.google.com/books?id=-2Ewg8QX8U4C&pg=PA183 |date=13 February 2012 |publisher=Cengage Learning |isbn=978-1-133-19024-0 |page=183}}</ref><ref name="Shibu">{{cite book |author=Shibu K. V. |title=Introduction to Embedded Systems |url=https://books.google.com/books?id=8hfn4gwR90MC&pg=PA402 |publisher=Tata McGraw-Hill Education |isbn=978-0-07-014589-4 |page=402}}</ref> When used with this definition, multiprocessing is sometimes contrasted with [[Computer multitasking|multitasking]], which may use just a single processor but switch it in time slices between tasks (i.e. a [[time-sharing system]]). Multiprocessing however means true parallel execution of multiple processes using more than one processor.<ref name="Shibu"/> Multiprocessing doesn't necessarily mean that a single process or task uses more than one processor simultaneously; the term [[Parallel computing|parallel processing]] is generally used to denote that scenario.<ref name="MorleyParker2012"/> Other authors prefer to refer to the operating system techniques as [[multiprogramming]] and reserve the term ''multiprocessing'' for the hardware aspect of having more than one processor.<ref name="EbbersKettner2012">{{cite book |author1=Mike Ebbers |author2=John Kettner |author3=Wayne O'Brien |author4=Bill Ogden |title=Introduction to the New Mainframe: z/OS Basics |url=https://books.google.com/books?id=c-a1AgAAQBAJ&pg=PA96 |year=2012 |publisher=IBM |isbn=978-0-7384-3534-3 |page=96}}</ref><ref name="Arora2006">{{cite book |author=Ashok Arora |title=Foundations of Computer Science |url=https://books.google.com/books?id=CrcoszZBMowC&pg=PA149 |year=2006 |publisher=Laxmi Publications |isbn=978-81-7008-971-1 |page=149}}</ref> The remainder of this article discusses multiprocessing only in this hardware sense.

In [[Flynn's taxonomy]], multiprocessors as defined above are [[Multiple instruction, multiple data|MIMD]] machines.<ref name="Giladi2008"/><ref name="Shiva2005">{{cite book |author=Sajjan G. Shiva |title=Advanced Computer Architectures |url=https://books.google.com/books?id=DhdCwk5AhbEC&pg=PA221 |date=20 September 2005 |publisher=CRC Press |isbn=978-0-8493-3758-1 |page=221}}</ref> As the term "multiprocessor" normally refers to tightly coupled systems in which all processors share memory, multiprocessors are not the entire class of MIMD machines, which also contains [[message passing]] multicomputer systems.<ref name="Giladi2008">{{cite book |author=Ran Giladi |title=Network Processors: Architecture, Programming, and Implementation |url=https://books.google.com/books?id=_7aH_4axpwAC&pg=PA293 |year=2008 |publisher=Morgan Kaufmann |isbn=978-0-08-091959-1 |page=293}}</ref>