Overclocking

Not to be confused with odometer.

In computing, overclocking is the practice of increasing the clock rate of computer components within a computer to exceed that certified by the manufacturer^[1]. Commonly, operating voltage is also increased to maintain a component's operational stability at accelerated speeds. Semiconductor devices operated at higher frequencies and voltages increase power consumption and heat.^[2] An overclocked device may be unreliable or fail completely if the additional heat load is not removed or power delivery components cannot meet increased power demands. Many device warranties state that overclocking or over-specification^[3] voids any warranty, but some manufacturers allow overclocking as long as it is done (relatively) safely.^[4]

Overclocking BIOS setup on an ABIT NF7-S motherboard with an AMD Athlon XP processor.

Overview

The purpose of overclocking is to increase the operating speed of a given component.^[5]

Underclocking

Main article: Underclocking

Conversely, the primary goal of underclocking is to reduce power consumption and the resultant heat generation of a device, with the trade-offs being lower clock speeds and reductions in performance. Reducing the cooling requirements needed to keep hardware at a given operational temperature has knock-on benefits such as lowering the number and speed of fans to allow quieter operation, and in mobile devices increase the length of battery life per charge. Some manufacturers underclock components of battery-powered equipment to improve battery life, or implement systems that detect when a device is operating under battery power and reduce clock frequency.^[6]

Underclocking and undervolting would be attempted on a desktop system to have it operate silently (such as for a home entertainment center) while potentially offering higher performance than currently offered by low-voltage processor offerings. This would use a "standard-voltage" part and attempt to run with lower voltages (while attempting to keep the desktop speeds) to meet an acceptable performance/noise target for the build. This was also attractive as using a "standard voltage" processor in a "low voltage" application avoided paying the traditional price premium for an officially certified low voltage version. However again like overclocking there is no guarantee of success, and the builder's time researching given system/processor combinations and especially the time and tedium of performing many iterations of stability testing need to be considered. The usefulness of underclocking (again like overclocking) is determined by what processor offerings, prices, and availability are at the specific time of the build. Underclocking is also sometimes used when troubleshooting.^[7]

Enthusiast culture

Overclocking has become more accessible with motherboard makers offering overclocking as a marketing feature on their mainstream product lines. However, the practice is embraced more by enthusiasts than professional users, as overclocking carries a risk of reduced reliability, accuracy and damage to data and equipment. Additionally, most manufacturer warranties and service agreements do not cover overclocked components nor any incidental damages caused by their use. While overclocking can still be an option for increasing personal computing capacity, and thus workflow productivity for professional users, the importance of stability testing components thoroughly before employing them into a production environment cannot be overstated.

Overclocking offers several draws for overclocking enthusiasts. Overclocking allows testing of components at speeds not currently offered by the manufacturer, or at speeds only officially offered on specialized, higher-priced versions of the product. A general trend in the computing industry is that new technologies tend to debut in the high-end market first, then later trickle down to the performance and mainstream market. If the high-end part only differs by an increased clock speed, an enthusiast can attempt to overclock a mainstream part to simulate the high-end offering. This can give insight on how over-the-horizon technologies will perform before they are officially available on the mainstream market, which can be especially helpful for other users considering if they should plan ahead to purchase or upgrade to the new feature when it is officially released.

Some hobbyists enjoy building, tuning, and "Hot-Rodding" their systems in competitive benchmarking competitions, competing with other like-minded users for high scores in standardized computer benchmark suites. Others will purchase a low-cost model of a component in a given product line, and attempt to overclock that part to match a more expensive model's stock performance. Another approach is overclocking older components to attempt to keep pace with increasing system requirements and extend the useful service life of the older part or at least delay purchase of new hardware solely for performance reasons. Another rationale for overclocking older equipment is even if overclocking stresses equipment to the point of failure earlier, little is lost as it is already depreciated, and would have needed to be replaced in any case.^[8]

Components

Considerations

Cooling

Main article: Computer cooling

High quality heat sinks are often made of copper.

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 fans, larger heat sinks, heat pipes 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.^[9] 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 pipes can be used to improve conductivity. Many heatsinks combine two or more materials to achieve a balance between performance and cost.^[9]

Interior of a water-cooled computer, showing CPU water block, tubing, and pump

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 refrigerators and can be adapted for computer use. Liquid nitrogen, liquid helium, and dry ice are used as coolants in extreme cases,^[10] 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^[11]) above 500 GHz, which was done by cooling the chip to 4.5 K (−268.6 °C; −451.6 °F) using liquid helium.^[12] Set in November 2012, the CPU Frequency World Record is 9008.82 MHz as of December 2022.^[13] 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.^[10] Moreover, silicon-based junction gate field-effect transistors (JFET) will degrade below temperatures of roughly 100 K (−173 °C; −280 °F) and eventually cease to function or "freeze out" at 40 K (−233 °C; −388 °F) since the silicon ceases to be semiconducting,^[14] 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.^[15][16]

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.^[17] 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.^[17]

Amateur overclocking enthusiasts have used a mixture of dry ice and a solvent with a low freezing point, such as acetone or isopropyl alcohol.^[18] This cooling bath, often used in laboratories, achieves a temperature of −78 °C (−108 °F).^[19]

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 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.^[20]

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.^[21]

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.^[22]

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 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".^[23]

Measuring effects of overclocking

Manufacturer and vendor overclocking

Overclocking is sometimes offered as a legitimate service or feature for consumers, in which a manufacturer or retailer tests the overclocking capability of processors, memory, video cards, and other hardware products. Several video card manufactures now offer factory-overclocked versions of their graphics accelerators, complete with a warranty, usually at a price intermediate between that of the standard product and a non-overclocked product of higher performance.

It is speculated that manufacturers implement overclocking prevention mechanisms such as CPU multiplier locking to prevent users from buying lower-priced items and overclocking them. These measures are sometimes marketed as a consumer protection benefit, but are often criticized by buyers.

Many motherboards are sold, and advertised, with extensive facilities for overclocking implemented in hardware and controlled by BIOS settings.^[24]

CPU multiplier locking

Advantages

Disadvantages

General

• Fan noise: High-performance fans running at maximum speed used for the required degree of cooling of an overclocked machine can be noisy, some producing 50 dB or more of noise. When maximum cooling is not required, in any equipment, fan speeds can be reduced below the maximum: fan noise has been found to be roughly proportional to the fifth power of fan speed; halving speed reduces noise by about 15 dB.^[25]
• An overclocked computer may become unreliable. For example: Microsoft Windows may appear to work with no problems, but when it is re-installed or upgraded, error messages may be received such as a "file copy error" during Windows Setup.^[26]

Risks of overclocking

• Increasing the operation frequency of a component will usually increase its thermal output in a linear fashion, while an increase in voltage usually causes thermal power to increase quadratically.^[27]

Limitations

Adaptive Management in Overclocking

Graphics cards

The BFG GeForce 6800GSOC ships with higher memory and clock rates than the standard 6800GS.

Graphics cards can also be overclocked. There are utilities to achieve this, such as EVGA's Precision, RivaTuner, AMD Overdrive (on AMD cards only), MSI Afterburner, Zotac Firestorm, and the PEG Link Mode on Asus motherboards. Overclocking a GPU will often yield a marked increase in performance in synthetic benchmarks, usually reflected in game performance.^[28]

Flashing

See also

• Electronics portal

• Clock rate
• CPU-Z
• Double boot
• Dynamic voltage scaling
• POWER8 on-chip controller (OCC)
• Serial presence detect (SPD)
• Super PI
• Underclocking
• UNIVAC I Overdrive, 1952 unofficial modification