Mods: perhaps remove this thread, since there are two of these nearly-identical ones? Either way, here is my post from the other one, C/P
Overclocking is the act of increasing the clock speed of your computer's components (such as your CPU, which might have a default clock speed of 2000mhz (2ghz), and pushing it to 2500mhz(2.5ghz))
Overclocking is primarely done via the BIOS for each motherboard, however it is not without risks. Many components are built to barely meet the specifications they have, for economy reasons, and pushing them beyond that will often cause them to fail. Also you will need *VERY* high quality cooling and power supplies to handle the increased demand, as the components will become less energy-efficient as they are pushed further beyond their normal usage limits. DO NOT attempt to overclock if your system is not *ROCK SOLID* stable to start with, and *DO NOT* do it on any vital system.
To overclock, first you need to know your current specs, I'd recommend using software like
Sandra to check on what the currently running specs of oyur hardware is (NB, Memory, CPU, GPU, etc.) Then start with researching your components, find the maximum they are officially rated for, for example, my memory (Crucial Balistix) was rated for 3-2-2-5 timings, but was runnning at 4-3-3-6 by my motherboards default. After confirming it was stable at that speed, I adjusted the motherboard to manual memory timings, and set the 3-2-2-5 timings, giving me about a 15% increase in memory throughput. The CPU I chose was an AMD 4000+, I researched and saw it's the same core used in the 4400+, and while the multiplier was locked, the FSB wasn't, so once I confirmed everything was stable, I slowly started raising my FSB 2mhz at a time (default was 200, moved to 202, rebooted, ran it for an hour, seemed good, move to 204, etc.) I would choose realtively frequent points for extended use testing, such as 210mhz for my FSB, and would run a week at that speed, making sure it was fine before moving up any more.
With good hardware and good cooling, you can usually manage about 30% above stock speeds. With very good hardware and exotic cooling (such as watercooling products from Thermaltake or Koolance) that can be almost 60%, and in rare cases 80%, but this is all at the risk of destroying your hardware and data.