How do You Get at the Extra Speed?
Much as the more you know about wood, the more likely you are to identify nicer pieces of wood, you will need to know a few things about your CPU to get the most out of it. Details vary for different kinds of CPU, and specific instructions will follow, but we will go over some general concepts now. Some motherboard manufacturers include software that allows you to overclock your computer from inside your operating system, but it is traditionally done via the BIOS. You enter the BIOS by pushing a key (usually Del, F1, or Esc) during the splash screen (the one that has the brand of PC or motherboard you own) of the boot up process.
We will use CPU-Z to help explain some concepts. The speed listed for a CPU (Core Speed) is found by taking a base Bus speed, multiplying it by the CPU’s data rate to get the Rated Bus (this can be called Front Side Bus for Core 2, HTT for AMD, etc.), and multiplying that by the CPU’s multiplier. Intel’s Extreme and AMD’s Black Edition CPUs have unlocked multipliers; their others do not. An unlocked multiplier allows for more flexibility when overclocking, but you pay a premium, a dear one on the Intel side in particular. Overclocking the CPU involves increasing the multiplier or bus speeds in small increments, then testing with software that really pushes your equipment to make sure it is stable.
Depending on how your CPU uses memory (the memory controller can be on the motherboard like in Core 2 or on the CPU like in Phenom or Core i7) and your BIOS options, overclocking a CPU may push the memory too hard. In some cases you may have to back off (underclock) your memory to get the best CPU and overall system performance. The easiest method to deal with this, if available, is to unlink (unsynch, etc., the terms change but the point is that you can change one and it won’t change the other) the CPU buses and memory speed. That way you can work on the CPU on its own, then you can enter your memory’s factory settings, or overclock it as well.
If the resulting proportion of memory and CPU speeds are close to one of the synch ratios offered in your BIOS, than it is worth locking them. This is one of the big advantages of an unlocked multiplier on the CPU; if your memory is holding back the bus speeds, you can increase the multiplier.
You can also overclock a GPU (video card), described here.