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Read here>>>http://www.wikihow.com/Overclock-a-PC

Overclocking is the process of making a computer or component operate faster than the clock frequency specified by the manufacturer by modifying system parameters. One of the most important techniques is running at a higher clock rate (more clock cycles per second; hence the name "overclocking"), but other parameters, such as CPU multiplier and memory timings, can also be changed and would be considered to be overclocking. Operating voltages may also be changed (increased), which can increase the speed at which operation remains stable. Most overclocking techniques increase power consumption, generating more heat, which must be dispersed if the chip is to remain operational.

The purpose of overclocking is to increase the operating speed of given hardware. The trade-offs are an increase in power consumption and fan noise, the system can become unstable if the equipment is overclocked too much, and the risk of damage due to excessive overvoltage or heat generation. In extreme cases costly and complex cooling (e.g., water-cooling) is required.

Conversely, underclocking trades off slower operation to reduce power consumption and temperature, cooling requirements (and therefore the number and speed of fans, allowing quiet operation) and, where relevant, increase battery life per charge. Some manufacturers underclock components of battery-powered equipment to improve battery life or implement systems that reduce the frequency when operating under battery.

On a large number of newer Intel CPUs (CPUs not marked with the letter K), because of the CPU's drastic redesign (to put it simply, replacement of the FSB with the base clock), overclocking - if even possible - comes with high risk of system instability. Undervolting is possible to some extent (depending on motherboard design and CPU quality) and may allow a user to turn a standard voltage CPU into a low voltage CPU without having to pay more, and not be restricted by low voltage CPU's low multiplier.

The speed gained by overclocking depends largely upon the application; benchmarks for different purposes are published. In some cases there is a simple speed gain and saving of time; in others a certain speed may be required for correct operation, as in displaying high-resolution video and playing games with fast action. The numerical gain varies, but is often of the order of 20%.

Many people overclock or 'rightclock' their hardware to improve its performance. This is practiced more by enthusiasts than professional users seeking an increase in the performance of their computers, as overclocking carries risks of less reliable functioning and damage. There are several purposes for overclocking. Overclocking allows testing over-the-horizon technologies that available component specifications are not capable of, without having to enter the expensive realm of specialized computing. For professional users, overclocking improves professional personal computing capacity, therefore allowing improved productivity. Hobbyists may enjoy building, tuning, and comparison racing their systems with standardized benchmark software. Some hobbyists purchase less expensive computer components and overclock to higher clock rates in an attempt to save money but achieve the same performance. A similar but slightly different approach to cost saving is overclocking outdated components to keep pace with new system requirements, rather than purchasing new hardware. If the overclocking stresses equipment to the point of failure, little is lost as it is fully depreciated, and would have needed to be replaced in any case.

Computer components that may be overclocked include processors (CPU), video cards, motherboard chipsets, and RAM. Most modern CPUs increase their effective operating speeds by multiplying the system clock frequency by a factor (the CPU multiplier). CPUs can be overclocked by manipulating the CPU multiplier, and the CPU and other components can be overclocked by increasing the speed of the system clock or other clocks (such as a front-side bus (FSB) clock). As clock speeds are increased components will ultimately stop operating reliably, or fail permanently, even if voltages are increased to maximum safe levels. The maximum speed is determined by overclocking beyond the point of instability, then accepting a slightly lower setting. Components are guaranteed to operate correctly up to their rated values; beyond there different samples may have different overclocking potential.

CPU multipliers, bus dividers, voltages, thermal loads, cooling techniques and several other factors such as individual semiconductor clock and thermal tolerances can affect the speed, stability, and safe operation of the computer.

Read more here>>>http://en.wikipedia.org/wiki/Overclocking

Noty much need to overclock anymore-- At one time software engineers were creating 'gameing' software that the CPU's of the time were a little slow so everyone serious about gaming would 'OC' their CPU's.  You could squeeze a few more GHz out of them, this was done either by adjusting the bios or by moving a few jumpers -- It worked in most cases but eventually if oc'd too much it would fry the CPU..  I did it many times.  Today it's not necessary. Most gaming is now gone to gaming platforms like X-box and playstation. I still dabble with some computer games but i have a 64bit system now and many of my older 'cherrished' games won't run at 64bit.