Out-of-order execution: Difference between revisions

Revision as of 12:27, 19 July 2025

Revision as of 22:22, 19 July 2025

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{{Use American English|date=January 2025}}

In [[computer engineering]], '''out-of-order execution''' (or more formally '''dynamic execution''') is an [[instruction scheduling]] paradigm used in high-performance [[central processing unit]]s to make use of [[instruction cycle]]s that would otherwise be wasted. In this paradigm, a processor executes [[Instruction (computing)|instructions]] in an order governed by the availability of input data and execution units,<ref>{{cite book |author-last=Kukunas |author-first=Jim |date=2015 |title=Power and Performance: Software Analysis and Optimization |url=https://books.google.com/books?id=X-WcBAAAQBAJ&pg=PA37 |publisher=Morgan Kaufman |page=37 |isbn=9780128008140}}</ref> rather than by their original order in a program.<ref>{{cite web |url=http://courses.cs.washington.edu/courses/csep548/06au/lectures/introOOO.pdf |title=Out-of-order execution |date=2006 |quote=don't wait for previous instructions to execute if this instruction does not depend on them |access-date=2014-01-17 |publisher=cs.washington.edu}}</ref><ref name="Regis High School 2011">{{cite web | title=The Centennial Celebration | website=Regis High School | date=2011-03-14 | url=https://www.regis.org/2014/multimedia/tomasulo.cfm | access-date=2022-06-25|quote=The algorithm "allows sequential instructions that would normally be stalled due to certain dependencies to execute non-sequentially" (also known as out of order execution).}}</ref> In doing so, the processor can avoid being idle while waiting for the preceding instruction to complete and can, in the meantime, process the next instructions that are able to run immediately and independently.<ref>{{cite web |url=http://www.pcguide.com/ref/cpu/arch/int/featOOE-c.html |url-status=dead |archive-url=https://web.archive.org/web/20190218182056/http://www.pcguide.com/ref/cpu/arch/int/featOOE-c.html |archive-date=2019-02-18 |quote=This flexibility improves performance since it allows execution with less 'waiting' time. |title=Out-of-order Execution |publisher=pcguideThe PC Guide |first=Charles M.com |last=Kozierok |date=April 17, 2001 |access-date=2014-01-17}}</ref>

== History ==