Overclocking

Overclocking is the process of forcing a computer component to run at a higher clock rate than it was designed for or was designated by the manufacturer.
Overclocking is usually practiced by PC enthusiasts in order to increase the performance of their computers. Some hardware enthusiasts purchase low-end computer components which they then overclock to higher speeds, while others overclock high-end components to attain levels of performance beyond original specifications.
Users who overclock their components mainly focus their efforts on processors, video cards, motherboard chipsets, and Random Access Memory (RAM).(en.wikipedia.org/wiki/Overclocking)

Consideration

There are several considerations when overclocking. Overclocking boosts the performance of a computer system by increasing clock frequencies, which requires certain precautions. The first consideration is to ensure that it is supplied with adequate power to operate at the new speed. However, supplying the power with improper settings or applying excessive voltage can permanently damage a component. Since tight tolerances are required for overclocking, only more expensive motherboards—with advanced settings that computer enthusiasts are likely to use—have built-in overclocking capabilities. Motherboards with fewer settings, such as those found in OEM systems, lack such features in order to eliminate the possibility of misconfiguration on behalf of an inept user and cut down on the support costs and warranty claims to the manufacturer.(en.wikipedia.org/wiki/Overclocking)

Cooling

All electronic circuits discharge heat generated by the movement of electrons. As clock frequencies in digital circuits increase, the temperature goes up. Due to the excessive heat produced by overclocked components, an effective cooling system is often necessary to avoid damaging the hardware. In addition, digital circuits slow down at high temperatures due to changes in MOSFET device characteristics. Wire resistance also increases slightly at higher temperatures, contributing to decreased circuit performance.
Because most stock cooling systems are designed for the amount of heat produced during non-overclocked use, overclockers typically turn to more effective cooling solutions, such as powerful fans or heavy duty heatsinks. Size, shape, and material all influence the ability of a heatsink to dissipate heat. Efficient heatsinks are often made entirely of thermally conductive copper, but these are often expensive.[1] Aluminum is more widely used material for heatsinks. Cast iron is the least expensive, but it should be avoided for its poor thermal conductivity. Many good-quality heatsink coolers combine two or more materials to maximize thermal conductivity while minimizing cost.
Water cooling and passive liquid coolant carrying waste heat to a radiator which is similar to an automobile engine's cooling system provide more effective cooling than heatsink and fan combinations when properly implemented, because liquid is denser than air and therefore offers greater thermal transference.
Thermoelectric cooling devices, also known as Peltier devices, are becoming more and more popular these days with the onset of high TDP processors from both Intel and AMD. TEC devices create temperature differences between two plates by running an electric current through said plates. This method of cooling is extremely effective, but is very inefficient, which leads to a lot of excess heat. Because of this, it is necessary to supplement TEC devices with a beefy convection-based heatsink or a water cooling system. Companies like Vigor Gaming offer all-in-one units that combine the advantages of TEC cooling with easy installation. One major drawback of TEC is that they have a large power overhead, sometimes drawing more than 60 W.Other cooling methods are forced convection and phase change cooling which is used in refrigerators. Submersion, liquid nitrogen and dry ice are used as a cooling method in extreme measures, such as record-setting attempts or one-off experiments rather than cooling an everyday system. Submersion method involves sinking a part of computer system directly into a chilled liquid substance that is thermally conductive but sufficiently low in electrical conductivity. The advantage of this technique is that no condensation can form on sensitive electronic components. A good submersion liquid is Fluorinert™ made by 3M, which is expensive and requires a permit to purchase it. Another option is mineral oil, but if it has impurities like water or scenting agents it will conduct electricity.
These extreme methods are generally intolerable in the long term, as they require refilling reservoirs of coolant or are noisy. Moreover, silicon-based MOSFETs will cease to function ("freeze out") below temperatures of roughly 100 K, so using extremely cold coolants may cause devices to cease functioning.(en.wikipedia.org/wiki/Overclocking)

Stabillity and functional correctness

An overclocked component operates outside of the manufacturer's recommended operating conditions, and as such may operate incorrectly, leading to system instability. An unstable overclocked system, while it may work fast, can be frustrating to use. Another risk is silent data corruption—errors that are initially undetected. 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 anyone but the processor manufacturer to thoroughly test the functionality of a processor. 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 flags; if the flags are not checked, the error will go undetected. Achieving good fault coverage requires immense engineering effort, and despite all the resources dedicated to validation by manufacturers, mistakes can still be made. To further complicate matters, in process technologies such as silicon on insulator, 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 speeds 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.[2]
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 a processor-intensive application for testing processors). Popular stress tests include Prime95, Super PI, SiSoftware Sandra, BOINC and Memtest86. The hope is that any functional-correctness issues with the overclocked component will show up during these tests, and if no errors are detected during the test, the component is then deemed "stable". Since fault coverage is important in stability testing, the tests are often run for long periods of time, hours or even days.(en.wikipedia.org/wiki/Overclocking)

Factors Allowing Overclocking

Overclockability arises in part due to the economics of the manufacturing processes of CPUs. In most cases, CPUs with different rated clock speeds are manufactured via exactly the same process. The clock speed that the CPU is rated for is the speed at which the CPU has passed the manufacturer's functionality tests when operating in worst-case conditions (for example, the highest allowed temperature and lowest allowed supply voltage). Manufacturers must also leave additional margin for reasons discussed below.
When a manufacturer rates a chip for a certain speed, it must ensure that the chip functions properly at that speed over the entire range of allowed operating conditions. When overclocking a system, the operating conditions are usually tightly controlled, making the manufacturer's margin available as free headroom. Other system components are generally designed with margins for similar reasons; overclocked systems absorb this designed headroom and operate at lower tolerances. Pentium architect Bob Colwell calls overclocking an "uncontrolled experiment in better-than-worst-case system operation".[3]
Some of what appears to be spare margin is actually required for proper operation of a processor throughout its lifetime. As semiconductor devices age, various effects such as hot carrier injection, negative bias thermal instability and electromigration reduce circuit performance. When overclocking a new chip it is possible to take advantage of this margin, but as the chip ages this can result in situations where a processor that has operated correctly at overclocked speeds for years spontaneously fails to operate at those same speeds later. If the overclocker is not actively testing for system stability when these effects become significant, errors encountered are likely to be blamed on sources other than the overclocking.(en.wikipedia.org/wiki/Overclocking)

Measuring Effects of Overclocking

Benchmarks are used to evaluate performance. The benchmarks can themselves 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 correct execution of the benchmark[citation needed]. 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).
Given only benchmark scores it may be difficult to judge the difference overclocking makes to the computing experience. For example, some benchmarks test only one aspect of the system, such as memory bandwidth, without taking into consideration how higher speeds in this aspect will improve the system performance as a whole[citation needed]. Apart from demanding applications such as video encoding, high-demand databases and scientific computing, memory bandwidth is typically not a bottleneck, so a great increase in memory bandwidth may be unnoticeable to a user depending on the applications they prefer to use. Other benchmarks, such as 3DMark attempt to replicate game conditions, but because some tests involve non-deterministic physics, such as ragdoll motion, the scene is slightly different each time and small differences in test score are overcome by the noise floor.(en.wikipedia.org/wiki/Overclocking)