Editing Hyper-threading (section)

{{short description|Proprietary simultaneous multithreading implementation by Intel}}
{{Use dmy dates|date=August 2020}}
[[File:Hyper-threaded CPU.png|thumb|upright=1.5|In this high-level depiction of HTT, instructions are fetched from RAM (differently colored boxes represent the instructions of four different [[Process (computing)|processes]]), decoded and reordered by the front end (white boxes represent [[Pipeline stall|pipeline bubbles]]), and passed to the execution core capable of executing instructions from two different programs during the same [[clock cycle]].<ref>{{cite web
 | url = https://arstechnica.com/features/2002/10/hyperthreading/1/
 | title = Introduction to Multithreading, Superthreading and Hyperthreading
 | date = 2002-10-03 | access-date = 2015-09-30
 | first = Jon | last = Stokes | website = [[Ars Technica]]
 | pages = 2&ndash;3
}}</ref><ref>{{cite web
 | url = http://www.cs.sfu.ca/~fedorova/Teaching/CMPT886/Spring2007/papers/hyper-threading.pdf
 | title = Hyper-Threading Technology Architecture and Microarchitecture
 | date = 2006-12-12
 | access-date = 2015-09-30
 | author1 = Deborah T. Marr
 | author2 = Frank Binns
 | author3 = David L. Hill
 | author4 = Glenn Hinton
 | author5 = David A. Koufaty
 | author6 = J. Alan Miller
 | author7 = Michael Upton
 | website = cs.sfu.ca
 | archive-url = https://web.archive.org/web/20150923211343/http://www.cs.sfu.ca/~fedorova/Teaching/CMPT886/Spring2007/papers/hyper-threading.pdf
 | archive-date = 23 September 2015
 | url-status = dead
 }}</ref><ref>{{cite web
 | url = http://www.anandtech.com/show/6355/intels-haswell-architecture/6
 | title = The Haswell Front End – Intel's Haswell Architecture Analyzed
 | date = 2012-10-05 | access-date = 2015-09-30
 | author = Anand Lal Shimpi | publisher = [[AnandTech]]
}}</ref>]]

'''Hyper-threading''' (officially called '''Hyper-Threading Technology''' or '''HT Technology''' and abbreviated as '''HTT''' or '''HT''') is [[Intel]]'s [[proprietary hardware|proprietary]] [[simultaneous multithreading]] (SMT) implementation used to improve [[parallel computation|parallelization of computations]] (doing multiple tasks at once) performed on [[x86]] microprocessors. It was introduced on [[Xeon]] server [[central processing unit|processors]] in February 2002 and on [[Pentium&nbsp;4]] desktop processors in November 2002.<ref>{{cite web |url=http://www.xbitlabs.com/articles/cpu/display/pentium4-3066.html |title=Intel Pentium&nbsp;4 3.06GHz CPU with Hyper-Threading Technology: Killing Two Birds with a Stone.. |publisher=X-bit labs |access-date=2014-06-04 |url-status=dead |archive-url=https://web.archive.org/web/20140531105602/http://www.xbitlabs.com/articles/cpu/display/pentium4-3066.html |archive-date=31 May 2014}}</ref> Since then, Intel has included this technology in [[Itanium]], [[Intel Atom|Atom]], and [[Intel Core|Core 'i' Series]] CPUs, among others.<ref>{{cite web 
|url=https://www.intel.co.uk/content/www/uk/en/architecture-and-technology/hyper-threading/hyper-threading-technology.html 
|title=Intel® Hyper-Threading Technology (Intel® HT Technology) 
|publisher=Intel 
|access-date=2021-10-24}}</ref>

For each [[processor core]] that is physically present, the [[operating system]] addresses two virtual (logical) cores and shares the workload between them when possible. The main function of hyper-threading is to increase the number of independent instructions in the pipeline; it takes advantage of [[Superscalar processor|superscalar]] architecture, in which multiple instructions operate on separate data [[Parallel computing|in parallel]]. With HTT, one physical core appears as two processors to the operating system, allowing [[Concurrent computing|concurrent]] scheduling of two processes per core. In addition, two or more processes can use the same resources: If resources for one process are not available, then another process can continue if its resources are available.

In addition to requiring simultaneous multithreading support in the operating system, hyper-threading can be properly utilized only with an operating system specifically optimized for it.<ref>[http://software.intel.com/en-us/articles/required-components-interchangeability-list-for-the-intel-pentiumr-4-processor-with-ht-technology Intel Required Components Interchangeability List for the Intel Pentium&nbsp;4 Processor with HT Technology], includes list of Operating Systems that include optimizations for Hyper-Threading Technology; they are Windows XP Professional&nbsp;64, Windows XP MCE, Windows XP Home, Windows XP Professional, some versions of Linux such as COSIX Linux&nbsp;4.0, RedHat Linux&nbsp;9 (Professional and Personal versions), RedFlag Linux Desktop&nbsp;4.0 and SuSe Linux&nbsp;8.2 (Professional and Personal versions)</ref>