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Maximum Clock Speed: The Right CPU Makes All The Difference

The Iceman Cometh: P4 at 4.1 GHz
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We had a choice of three different 3.06 GHz (factory rated) Pentium 4 CPUs at the start of our tests. After a number of trials, we realized that only two of these were suitable for extreme overclocking. One sample packed up after the 3.8 GHz mark - even with a cooling temperature of minus 52 degrees Celsius. In contrast, the top performer (which looks no different externally to the other 3 GHz processors) achieves a speed of 4,122 MHz and remains stable running Windows XP.

Thanks to efficient cooling, the temperature of the CPU die is able to reach minus 10 degrees Celsius.

Voltage Matters: Too Much Doesn't Help


The settings for clockspeed beyond 4000 MHz with the Pentium 4.

The 3.06 GHz P4 is designed to operate at 1.550 V. As a general rule, the quality of the signal within the CPU deteriorates as the CPU speed is increased. To allow the processor to run at higher speeds, you can improve the switching characteristics of the transistors by increasing the voltage in small steps. This does mean, however, that some transistors will then operate beyond their specification, which will reduce their service life. Moreover, increasing the voltage increases power consumption, and the power dissipation increases by the power of two. The effect is immediately recognizable, because the processor becomes very hot and needs a special form of cooling.

Some seasoned overclockers are of the opinion that a significant increase in the core voltage provides the best conditions for overclocking. Hands-on experience in our labs has shown that this is not necessarily so. What is required is the correct relationship between core voltage (as well as consequent power consumption and dissipation) and clock speed, assuming, of course, that adequate cooling is available. This observation is, admittedly, only valid for extreme processor speeds above 4 GHz or an overclock by at least 30%. A 2.4 GHz processor is a completely different animal than a P4 CPU that has already been clocked higher at the factory.

In the lab we discovered that increasing the core voltage above 1.850 V provided no additional stability.

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