The basics of CPU overclocking

Pushing your processor to new heights can be extremely rewarding—if all goes right. Take the time to understand the concepts of overclocking and the factors that can affect success.


DETERMINING A CPU’S SPEED

There’s simple math that determines the clock speed of any CPU. Each CPU has a fi xed internal number called the clock multiplier. That number multiplied by the reference clock of the front-side bus determines the stated clock speed of the processor. For example, an Intel 2.66GHz Core 2 Quad Q6700 has a clock multiplier of 10. The stock system bus speed for this processor is 1,066MHz. But wait, 1,066MHz multiplied by 10 equals 10GHz. What gives? Intel’s front-side bus is quad-pumped, so its actual reference clock is 266MHz (1,066MHz divided by four). That makes the clock speed of a Core 2 Quad Q6700 10 times 266MHz for 2,660MHz, or 2.66GHz. This same math applies to AMD’s Athlon 64 CPUs, although, technically, they have no front-side bus; instead, a HyperTransport link connects the CPU to the chipset. A 2.6GHz Athlon 64 X2 5000+, for example, operates on a 13x multiplier using a 200MHz link—the actual HyperTransport link connection runs at 1GHz, as it operates on a 5x multiplier. You can overclock both Intel and AMD CPUs by increasing the multiplier setting, increasing the “front-side bus,” or both. By using a combination of a multiplier and FSB overclock, you may achieve higher speeds with more stability. Depending on your situation, a combination of both may give you the best overclock, as your motherboard may simply not be up to running at excessively high speeds.

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