Let me give it a shot. The speed of a CPU is a certain multiple of the front side bus (FSB). So for example, a CPU rated at 1.4 GHz could be running at 133x10.5 (133 being the FSB and 10.5 being the multiple). So, you can overclock a CPU by either raising the FSB or the multiplier. I believe newer CPUs have "locked" multipliers, so most people just overclock by raising the FSB. This is done by doing into the BIOS of your motherboard. Overclocking success is dependent on the CPU, the motherboard, the quality of the memory, and the efficacy of the CPU's heatsink/fan.
I may have just spewed a whole load of crap, but the above should be more or less accurate

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