Editing Overclocking (section)

==Considerations==
There are several things to be considered when overclocking. First is to ensure that the component is supplied with adequate power at a voltage sufficient to operate at the new [[clock rate]]. Supplying the power with improper settings or applying excessive [[voltage]] can permanently damage a component.

In a professional production environment, overclocking is only likely to be used where the increase in speed justifies the cost of the expert support required, the possibly reduced reliability, the consequent effect on maintenance contracts and warranties, and the higher power consumption. If faster speed is required it is often cheaper when all costs are considered to buy faster hardware.

=== Cooling ===
{{Main|Computer cooling}}
[[Image:Copper heat sink with pipes.jpg|thumb|High quality [[heat sink]]s are often made of [[copper]].]]

All [[Electrical network|electronic circuits]] produce heat generated by the movement of electric current. As clock frequencies in [[digital circuit]]s and voltage applied increase, the heat generated by components running at the higher performance levels also increases. The relationship between clock frequencies and [[thermal design power]] (TDP) are linear. However, there is a limit to the maximum frequency which is called a "wall". To overcome this issue, overclockers raise the chip voltage to increase the overclocking potential. Voltage increases power consumption and consequently heat generation significantly (proportionally to the square of the voltage in a linear circuit, for example); this requires more cooling to avoid damaging the hardware by overheating. In addition, some digital circuits slow down at high temperatures due to changes in [[MOSFET]] device characteristics. Conversely, the overclocker may decide to ''decrease'' the chip voltage while overclocking (a process known as undervolting), to reduce heat emissions while performance remains optimal.

Stock cooling systems are designed for the amount of power produced during non-overclocked use; overclocked circuits can require more cooling, such as by powerful [[fan (mechanical)|fans]], larger [[heat sink]]s, [[heat pipe]]s and [[water cooling]]. Mass, shape, and material all influence the ability of a heatsink to dissipate heat. Efficient heatsinks are often made entirely of [[copper]], which has high [[thermal conductivity]], but is expensive.<ref name=Wainner38>{{cite book | title = The Book of Overclocking | first1 = Scott | last1 = Wainner | first2 = Robert |last2=Richmond | page = [https://archive.org/details/bookofoverclocki0000wain/page/38 38] | isbn = 978-1-886411-76-0 | publisher = No Starch Press | year = 2003 | url = https://archive.org/details/bookofoverclocki0000wain/page/38 }}</ref> [[Aluminium]] is more widely used; it has good thermal characteristics, though not as good as copper, and is significantly cheaper. Cheaper materials such as steel do not have good thermal characteristics. [[Heat pipe]]s can be used to improve conductivity. Many heatsinks combine two or more materials to achieve a balance between performance and cost.<ref name=Wainner38/>

[[File:DIY PC watercooling T-Line.JPG|Interior of a water-cooled computer, showing CPU [[water block]], tubing, and pump|left|thumb]]

Water cooling carries [[waste heat]] to a [[radiator]]. [[Thermoelectric cooling]] devices which actually refrigerate using the [[Peltier effect]] can help with high [[thermal design power]] (TDP) processors made by Intel and AMD in the early twenty-first century. Thermoelectric cooling devices create temperature differences between two plates by running an [[electric current]] through the plates. This method of cooling is highly effective, but itself generates significant heat elsewhere which must be carried away, often by a convection-based heatsink or a [[water cooling#Computer usage|water cooling]] system.

[[Image:2007TaipeiITMonth IntelOCLiveTest Overclocking-6.jpg|right|thumb|[[Liquid nitrogen]] may be used for cooling an overclocked system, when an extreme measure of cooling is needed.]]

Other cooling methods are [[forced convection]] and [[phase transition]] cooling which is used in [[refrigerator]]s and can be adapted for computer use. [[Liquid nitrogen]], [[liquid helium]], and [[dry ice]] are used as coolants in extreme cases,<ref name=Wainner44>{{cite book | title = The Book of Overclocking | first1 = Scott | last1 = Wainner | first2 = Robert |last2=Richmond | page = [https://archive.org/details/bookofoverclocki0000wain/page/44 44] | isbn = 978-1-886411-76-0 | publisher = No Starch Press | year = 2003 | url = https://archive.org/details/bookofoverclocki0000wain/page/44 }}</ref> such as record-setting attempts or one-off experiments rather than cooling an everyday system. In June 2006, [[IBM]] and [[Georgia Institute of Technology]] jointly announced a new record in silicon-based chip [[clock rate]] (the rate a transistor can be switched at, not the CPU clock rate<ref>{{cite web|last=Stokes|first=Jon|title=IBM's 500GHz processor? Not so fast…|url=https://arstechnica.com/uncategorized/2006/06/7117-2/|website=Ars Technica|date=22 June 2006|access-date=14 June 2017|archive-date=20 October 2017|archive-url=https://web.archive.org/web/20171020190922/https://arstechnica.com/uncategorized/2006/06/7117-2/|url-status=live}}</ref>) above 500&nbsp;GHz, which was done by cooling the chip to {{Convert|4.5|K|C F|1|lk=on}} using liquid helium.<ref>{{cite web| last = Toon| first = John| date = 20 June 2006| url = http://gtresearchnews.gatech.edu/georgia-techibm-team-demonstrates-first-500-ghz-silicon-germanium-transistors/| title = Georgia Tech/IBM Announce New Chip Speed Record| publisher = Georgia Institute of Technology| access-date = 2 February 2009| url-status = dead| archive-url = https://web.archive.org/web/20100701230256/http://gtresearchnews.gatech.edu/georgia-techibm-team-demonstrates-first-500-ghz-silicon-germanium-transistors/| archive-date = 1 July 2010}}</ref> Set in November 2012, the CPU Frequency World Record is 9008.82&nbsp;MHz as of December 2022.<ref>{{cite web |title=Intel Core i9 13900K Breaks the CPU Frequency World Record |url=https://valid.x86.fr/t14i1f |url-status=live |archive-url=https://web.archive.org/web/20180302225606/https://valid.x86.fr/t14i1f |archive-date=2018-03-02 |access-date=2022-12-09}}</ref> These extreme methods are generally impractical in the long term, as they require refilling reservoirs of vaporizing coolant, and [[condensation]] can form on chilled components.<ref name=Wainner44/> Moreover, [[silicon]]-based [[junction gate field-effect transistor]]s (JFET) will degrade below temperatures of roughly {{convert|100|K|C F|0}} and eventually cease to function or "freeze out" at {{convert|40|K|C F|0}} since the silicon ceases to be semiconducting,<ref>{{cite web | title = Extreme-Temperature Electronics: Tutorial – Part 3 | url = http://www.extremetemperatureelectronics.com/tutorial3.html | year = 2003 | access-date = 2007-11-04 | archive-date = 2012-03-06 | archive-url = https://web.archive.org/web/20120306214055/http://www.extremetemperatureelectronics.com/tutorial3.html | url-status = live }}</ref> so using extremely cold coolants may cause devices to fail. [[Blowtorch]] is used to temporarily raise temperature to issues of over-cooling when not desirable.<ref>{{Cite news |author1=Wes Fenlon |date=2017-06-09 |title=Overclocking a CPU to 7 GHz with the science of liquid nitrogen |language=en |work=PC Gamer |url=https://www.pcgamer.com/overclocking-a-cpu-to-7-ghz-with-the-science-of-liquid-nitrogen/ |access-date=2023-11-12}}</ref><ref>{{Cite web |date=2019-08-08 |title=Overclocking to 7GHz takes more than just liquid nitrogen |url=https://www.engadget.com/2017-06-04-gskill-hwbot-overclocking-workshop-7ghz-computex.html |access-date=2023-11-12 |website=Engadget |language=en-US}}</ref>

Submersion cooling, used by the [[Cray-2]] [[supercomputer]], involves sinking a part of computer system directly into a chilled liquid that is thermally conductive but has low [[electrical conductivity]]. The advantage of this technique is that no condensation can form on components.<ref name=Wainner48/> A good submersion liquid is [[Fluorinert]] made by [[3M]], which is expensive. Another option is [[mineral oil]], but impurities such as those in water might cause it to conduct electricity.<ref name=Wainner48>{{cite book | title = The Book of Overclocking | first = Scott | last = Wainner | author2 = Robert Richmond | page = [https://archive.org/details/bookofoverclocki0000wain/page/48 48] | isbn = 978-1-886411-76-0 | publisher = No Starch Press | year = 2003 | url = https://archive.org/details/bookofoverclocki0000wain/page/48 }}</ref>

Amateur overclocking enthusiasts have used a mixture of [[dry ice]] and a solvent with a low freezing point, such as [[acetone]] or [[isopropyl alcohol]].<ref>{{cite web |url=https://www.techpowerup.com/forums/threads/overclocking-with-dry-ice.101545/ |title=overclocking with dry ice! |work=TechPowerUp Forums |date=August 13, 2009 |access-date=January 7, 2020 |archive-date=December 7, 2019 |archive-url=https://web.archive.org/web/20191207134408/https://www.techpowerup.com/forums/threads/overclocking-with-dry-ice.101545/ |url-status=live }}</ref> This [[cooling bath]], often used in laboratories, achieves a temperature of {{convert|−78|C}}.<ref>[http://chemwiki.ucdavis.edu/VV_Lab_Techniques/Cooling_baths Cooling baths – ChemWiki] {{Webarchive|url=https://web.archive.org/web/20120828144459/http://chemwiki.ucdavis.edu/VV_Lab_Techniques/Cooling_baths |date=2012-08-28 }}. Chemwiki.ucdavis.edu. Retrieved on 2013-06-17.</ref> However, this practice is discouraged due to its safety risks; the solvents are flammable and volatile, and dry ice can cause [[frostbite]] (through contact with exposed skin) and suffocation (due to the large volume of [[carbon dioxide]] generated when it sublimes).

=== Stability and functional correctness ===

{{See also| Stress testing#Hardware }}

As an overclocked component operates outside of the manufacturer's recommended operating conditions, it may function incorrectly, leading to system instability. Another risk is [[Reliability, availability and serviceability (computer hardware)|silent data corruption]] by undetected errors. Such failures might never be correctly diagnosed and may instead be incorrectly attributed to software bugs in applications, [[device drivers]], or the operating system. Overclocked use may permanently damage components enough to cause them to misbehave (even under normal operating conditions) without becoming totally unusable.

A large-scale 2011 field study of hardware faults causing a system crash for consumer PCs and laptops showed a four to 20 times increase (depending on CPU manufacturer) in system crashes due to CPU failure for overclocked computers over an eight-month period.<ref>{{cite conference|url=http://research.microsoft.com/pubs/144888/eurosys84-nightingale.pdf|title=Cycles, cells and platters: an empirical analysis of hardware failures on a million consumer PCs.|conference=Proceedings of the sixth conference on Computer systems (EuroSys '11).|pages=343–356|year=2011|access-date=2012-12-05|archive-date=2012-11-14|archive-url=https://web.archive.org/web/20121114111006/http://research.microsoft.com/pubs/144888/eurosys84-nightingale.pdf|url-status=live}}</ref>

In general, overclockers claim that testing can ensure that an overclocked system is stable and functioning correctly. Although software tools are available for testing hardware stability, it is generally impossible for any private individual to thoroughly test the functionality of a processor.<ref>{{cite journal | citeseerx = 10.1.1.62.9086 | title = Coverage Metrics for Functional Validation of Hardware Designs | publisher = IEEE Design & Test of Computers | year = 2001 | first1 = Serdar |last1=Tasiran |first2=Kurt |last2=Keutzer}}</ref> Achieving good [[fault coverage]] requires immense engineering effort; even with all of the resources dedicated to validation by manufacturers, faulty components and even design faults are not always detected.

A particular "stress test" can verify only the functionality of the specific instruction sequence used in combination with the data and may not detect faults in those operations. For example, an arithmetic operation may produce the correct result but incorrect [[status register|flags]]; if the flags are not checked, the error will go undetected.

To further complicate matters, in process technologies such as [[silicon on insulator]] (SOI), devices display [[hysteresis]]—a circuit's performance is affected by the events of the past, so without carefully targeted tests it is possible for a particular sequence of state changes to work at overclocked rates in one situation but not another even if the voltage and temperature are the same. Often, an overclocked system which passes stress tests experiences instabilities in other programs.<ref>{{cite web | url = http://blogs.msdn.com/oldnewthing/archive/2005/04/12/407562.aspx | first = Raymond | last = Chen | title = The Old New Thing: There's an awful lot of overclocking out there | date = April 12, 2005 | access-date = 2007-03-17 | archive-date = 2007-03-08 | archive-url = https://web.archive.org/web/20070308074036/http://blogs.msdn.com/oldnewthing/archive/2005/04/12/407562.aspx | url-status = dead }}</ref>

In overclocking circles, "stress tests" or "torture tests" are used to check for correct operation of a component. These workloads are selected as they put a very high load on the component of interest (e.g. a graphically intensive application for testing video cards, or different math-intensive applications for testing general CPUs). Popular stress tests include [[Prime95]], [[Superpi]], OCCT, [[AIDA64]], [[Linpack]] (via the LinX and IntelBurnTest [[GUI]]s), SiSoftware Sandra, [[BOINC]], Intel Thermal Analysis Tool and [[Memtest86]]. The hope is that any functional-correctness issues with the overclocked component will manifest themselves during these tests, and if no errors are detected during the test, then the component is deemed "stable". Since fault coverage is important in [[Software testing|stability testing]], the tests are often run for long periods of time, hours or even days. An overclocked computer is sometimes described using the number of hours and the stability program used, such as "prime 12 hours stable".

===Factors allowing overclocking===
Overclockability arises in part due to the economics of the manufacturing processes of CPUs and other components. In many cases components are manufactured by the same process, and tested after manufacture to determine their actual maximum ratings. Components are then marked with a rating chosen by the market needs of the semiconductor manufacturer. If [[Semiconductor device fabrication#Device test|manufacturing yield]] is high, more higher-rated components than required may be produced, and the manufacturer may mark and sell higher-performing components as lower-rated for marketing reasons. In some cases, the true maximum rating of the component may exceed even the highest rated component sold. Many devices sold with a lower rating may behave in all ways as higher-rated ones, while in the worst case operation at the higher rating may be more problematical.

Notably, higher clocks must always mean greater waste heat generation, as semiconductors set to high must dump to ground more often. In some cases, this means that the chief drawback of the overclocked part is far more heat dissipated than the maximums published by the manufacturer. Pentium architect [[Bob Colwell]] calls overclocking an "uncontrolled experiment in better-than-worst-case system operation".<ref>{{cite journal|first1=Bob|last1=Colwell|title=The Zen of Overclocking|journal=[[Computer (magazine)|Computer]]|volume=37|issue=3|date=March 2004|pages=9–12|publisher=[[Institute of Electrical and Electronics Engineers]]|doi=10.1109/MC.2004.1273994|s2cid=21582410}}</ref>

=== Measuring effects of overclocking ===
{{Unreferenced section|date=October 2022}}
[[Benchmark (computing)|Benchmarks]] are used to evaluate performance, and they can become a kind of "sport" in which users compete for the highest scores. As discussed above, stability and functional correctness may be compromised when overclocking, and meaningful benchmark results depend on the correct execution of the benchmark. Because of this, benchmark scores may be qualified with stability and correctness notes (e.g. an overclocker may report a score, noting that the benchmark only runs to completion 1 in 5 times, or that signs of incorrect execution such as display corruption are visible while running the benchmark). A widely used test of stability is Prime95, which has built-in error checking that fails if the computer is unstable.

Using only the benchmark scores, it may be difficult to judge the difference overclocking makes to the overall performance of a computer. For example, some benchmarks test only one aspect of the system, such as memory [[Bandwidth (computing)|bandwidth]], without taking into consideration how higher [[clock rate]]s in this aspect will improve the system performance as a whole. Apart from demanding applications such as video encoding, high-demand [[database]]s and [[scientific computing]], [[memory bandwidth]] is typically not a [[bottleneck (engineering)|bottleneck]], so a great increase in memory bandwidth may be unnoticeable to a user depending on the applications used. Other benchmarks, such as [[3D Mark|3DMark]], attempt to replicate game conditions.