To overclock you must have adequate cooling.
Getting higher performance out of your current CPU can be done by overclocking - overclocking is dangerous and should only be attempted in small incremental steps/stages.
Overclocking voids hardware warranty, can damage hardware or can make a system unstable.
First you look at your temperature, for most modern CPU's if your temperature is around 30 - 40 degrees when idle it will increase to 37 - 46 under a heavier load. I personally wouldn't overclock if my CPU doesn't fit within these boundaries, my XP2500+ has a temperature that is too high and thus I don't overclock.
Overclocking will reduce the lifespan of your hardware.
Down to it.
Overclocking can be done in 2 main ways.
Firstly raising the FSB speed by a few MHz and letting the multiplier do its job.
Example, say you have a AMD Athlon XP3200+ (2.2GHz) with a FSB speed of originally 200MHz (in BIOS) and a multiplier at 11, giving a total GHz of 2.2, 11 x 200MHz = 2200MHz (2.2GHz) .
Increasing this FSB speed to 205MHz BIOS will give you:
205MHz x multiplier of 11 = 2255MHz (2.26GHz)
Simple see! A problem you might encounter is that your system becomes unstable, to make the CPU stable again you should give it more power, i.e. increase the voltage, from 1.65V (default for the XP3200+) to 1.675V or maybe 1.7V.
Increasing the voltage substantially increases the temperature depending on what cooling solution you have.
Repeat these steps until you have a satisfactory speed and temperature, and hopefully a stable system.
Increasing the multiplier instead of the FSB speed. Quite simple.
Using the same processor as above we can increase the multiplier from 11 to 11.5.
11.5 x 200MHz = 2.3GHz
The bad thing about this way is that it isn't as accurate as the steps above. Some people use a mixture of both, increasing the FSB and the multiplier... [size=4.5]carefully![/size]
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