Practice of increasing the clock rate of a computer to exceed that certified by the manufacturer
In computing, overclocking is the practice of increasing the clock rate of a computer to exceed that certified by the manufacturer. 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. 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 voids any warranty, but some manufacturers allow overclocking as long as it is done (relatively) safely.
Overview.
The purpose of overclocking is to increase the operating speed of a given component. Normally, on modern systems, the target of overclocking is increasing the performance of a major chip or subsystem, such as the main processor or graphics controller, but other components, such as system memory (RAM) or system buses (generally on the motherboard), are commonly involved. The trade-offs are an increase in power consumption (heat), fan noise (cooling), and shortened lifespan for the targeted components. Most components are designed with a margin of safety to deal with operating conditions outside of a manufacturer's control; examples are ambient temperature and fluctuations in operating voltage. Overclocking techniques in general aim to trade this safety margin by setting the device to run in the higher end of the margin, with the understanding that temperature and voltage must be more strictly monitored and controlled by the user. Examples are that operating temperature would need to be more strictly controlled with increased cooling, as the part will be less tolerant of increased temperatures at higher speeds. Also base operating voltage may be increased to compensate for unexpected voltage drops and to strengthen signaling and timing signals, as low-voltage excursions are more likely to cause malfunctions at higher operating speeds.
While most modern devices are fairly tolerant of overclocking, all devices have finite limits. Generally, for any given voltage most parts will have a maximum "stable" speed where they still operate correctly. Past this speed, the device starts giving incorrect results, which can cause malfunctions and sporadic behavior in any system depending on it. While in a PC context, the usual result is a system crash, more subtle errors can go undetected, which over a long enough time can give unpleasant surprises such as data corruption (incorrectly calculated results, or worse "writing to storage" incorrectly) or the system failing only during certain specific tasks (general usage such as internet browsing and word processing appear fine, but any application wanting advanced graphics crashes the system. There might also be a chance for damage to the hardware itself).
At this point, an increase in operating voltage of a part may allow more headroom for further increases in clock speed, but the increased voltage can also significantly increase heat output, as well as shorten the lifespan further. At some point, there will be a limit imposed by the ability to supply the device with sufficient power, the user's ability to cool the part, and the device's own maximum voltage tolerance before it achieves destructive failure. Overzealous use of voltage or inadequate cooling can rapidly degrade a device's performance to the point of failure, or in extreme cases outright destroy it.
The speed gained by overclocking depends largely upon the applications and workloads being run on the system, and what components are being overclocked by the user; benchmarks for different purposes are published.
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.
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.
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.
Components.
Technically any component that uses a timer (or clock) to synchronize its internal operations can be overclocked. Most efforts for computer components however focus on specific components, such as, processors (a.k.a. CPU), video cards, motherboard chipsets, and RAM. Most modern processors derive their effective operating speeds by multiplying a base clock (processor bus speed) by an internal multiplier within the processor (the CPU multiplier) to attain their final speed.
Computer processors generally are overclocked by manipulating the CPU multiplier if that option is available, but the processor and other components can also be overclocked by increasing the base speed of the bus clock. Some systems allow additional tuning of other clocks (such as a system clock) that influence the bus clock speed that, again is multiplied by the processor to allow for finer adjustments of the final processor speed.
Most OEM systems do not expose to the user the adjustments needed to change processor clock speed or voltage in the BIOS of the OEM's motherboard, which precludes overclocking (for warranty and support reasons). The same processor installed on a different motherboard offering adjustments will allow the user to change them.
Any given component will ultimately stop operating reliably past a certain clock speed. Components will generally show some sort of malfunctioning behavior or other indication of compromised stability that alerts the user that a given speed is not stable, but there is always a possibility that a component will permanently fail without warning, even if voltages are kept within some pre-determined safe values. The maximum speed is determined by overclocking to the point of first instability, then accepting the last stable slower setting. Components are only guaranteed to operate correctly up to their rated values; beyond that different samples may have different overclocking potential. The end-point of a given overclock is determined by parameters such as available CPU multipliers, bus dividers, voltages; the user's ability to manage thermal loads, cooling techniques; and several other factors of the individual devices themselves such as semiconductor clock and thermal tolerances, interaction with other components and the rest of the system.
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.
All electronic circuits produce heat generated by the movement of electric current. As clock frequencies in digital circuits 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 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. 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.
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 system.
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, such as record-setting attempts or one-off experiments rather than cooling an everyday system. In June 2006, IBM and Georgia Institute of