Overclocking

      Overclocking is, as most of us know, the process of tweaking a CPU or graphic card so that it runs faster than what it is rated at by its manufacturer. For example, you can overclock a CPU that runs at 3GHz to 3.6GHz or more and get more performance from the overclocked CPU.
      Overclocking is the process of running a computer component at a higher clock rate (more clock cycles per second) than it was designed for or was specified by the manufacturer, usually practiced by enthusiasts seeking an increase in the performance of their computers. Some purchase low-end computer components which they then overclock to higher clock rates, or overclock high-end components to attain levels of performance beyond the specified values. Others overclock outdated components to keep pace with new system requirements, rather than purchasing new hardware.
       People who overclock their components mainly focus their efforts on processors, video cards, motherboard chipsets, and RAM. It is done through manipulating the CPU multiplier and the motherboard's front-side bus (FSB) clock rate until a maximum stable operating frequency is reached, although with the introduction of Intel's new X58 chipset and the Core i7 processor, the front side bus has been replaced with the QPI (Quick Path Interconnect); often this is called the Baseclock (BCLK). While the idea is simple, variation in the electrical and physical characteristics of computing systems complicates the process. CPU multipliers, bus dividers, voltages, thermal loads, cooling techniques and several other factors such as individual semiconductor clock and thermal tolerances can affect it.
FSB × Multiplier = Frequency
     There are several considerations when overclocking. First is to ensure that the component is supplied with adequate power to operate at the new clock rate. 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 features, such as those found in original equipment manufacturer (OEM) systems, often do not support overclocking.Because overclocking increases the CPU speed and that naturally increases the load on the PSU. When overclocking, the user may have to increase the CPU voltage to attain high overclocks and stability. This further puts burden on the PSU and it should be capable of providing the required amount of power to all the components while still producing acceptable amount of ripple. Substandard PSUs may burst while overclocking and that can permanently damage components.
      The second thing you must look into is temperature. If you want to overclock, it is recommended that you use a third party cooler to cool your CPU as the stock heat sink is only capable of handling stock speeds. If you are increasing the CPU voltage, you will see an exponential increase in temperature and your cooler should be able to dissipate the heat generated. There are many third party coolers available for CPU in the market. All electronic circuits produce heat generated by the movement of electrical 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. The relationship between chip voltage and TDP is exponential due to the fact that as the chip warms, the resistance increases. This increased heat requires effective cooling to avoid damaging the hardware. In addition, some digital circuits slow down at high temperatures due to changes in MOSFET device characteristics. Because most stock cooling systems are designed for the amount of power produced during non-overclocked use, overclockers typically turn to more effective cooling solutions, such as powerful fans, larger heat sinks, heat pipes and water cooling. Size, 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 poorer thermal conductivity, but is significantly cheaper than copper. Heat pipes are commonly used to improve conductivity. Many heatsinks combine two or more materials to achieve a balance between performance and cost.

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

Water cooling carries waste heat to a radiator. Thermoelectric cooling devices, also known as Peltier devices, are recently popular with the onset of high thermal design power (TDP) processors made by Intel and AMD. 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. For this reason, it is often necessary to supplement thermoelectric cooling devices with a convection-based heatsink or a water-cooling system.

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 change 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 Technology jointly announced a new record in silicon-based chip clock rate above 500 GHz, which was done by cooling the chip to 4.5 K (−268.7 °C; −451.6 °F) using liquid helium. These extreme methods are generally impractical in the long term, as they require refilling reservoirs of vaporizing coolant, and condensation can be formed on chilled components. 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 so using extremely cold coolants may cause devices to fail.
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. A good submersion liquid is Fluorinert made by 3M, which is expensive and can only be purchased with a permit. Another option is mineral oil, but impurities such as those in water might cause it to conduct electricity.
When overclocking, you may be tempted to straightaway increase the FSB to see high overclocks. But it's always recommended to increase it in increments. Usually you will be doing that in BIOS and for each and every increment, you will have to boot into OS and see if the overclocked CPU can handle the desktop. You should also run a stress test to make sure the CPU handles the overclock well. OCCT is one of the best tools to check for CPU stability and you can also use the graphs it provides after the test is complete to assess important factors like temperature, ripple etc. You can also see if the CPU throttles during the test. Typically, the system will crash if the overclock isn't stable.
Overclocking is safe provided you take all the necessary steps prior to attempting and you can see the difference in games, media conversion and benchmarks. But it also voids warranty and if you are willing to take that risk, you can overclock and get more performance.