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Voltages and Temperatures

Every overclocker knows that one of the integral factors for successful CPU overclocking is the voltage increase for different parts of the platform. For example, when you overclock an LGA775 system, you often have to raise the processor core voltage, memory voltage, processor bus voltage and chipset voltage. Setting these parameters above their nominal values almost always improves the overclocking potential of the system. Although, you should also keep in mind that higher voltage in semiconductor components results in higher heat dissipation and logically, lower life span of these components. However, using a high-quality cooling system and increasing the nominal voltages to reasonable heights allows the user to find a compromise between so called “risk factors” and frequency potential increase.

The same is true for the new generation platforms. However, Core i7 based systems have different structure that is why their voltage management during overclocking experiments requires a completely different approach. Since the chipset North Bridge and processor bus have lost their determinative role, their voltages do not need to be adjusted in most cases, even when the frequencies get pushed up fairly high. However, the memory controller, which has migrated into the processor, and L3 cache now receive their power supply independently, so playing with it may actually pay back during overclocking.

So, there are four major voltages to work with during Core i7 overclocking. They are:

  • Processor core voltage of the actual CPU cores. The nominal setting for this parameter depends on the particular processor model, but it usually equals 1.2V. according to the specification, the maximum possible setting can be 1.55V, however, in this case you need nothing less than a water-cooling system involved.
  • Uncore voltage of the QPI controller built into the CPU and the L3 cache. Their default voltages are set at 1.2V, however, the specification claims that they can be increased up to 1.35V without any harm done to the processor.
  • Memory voltage. Although this voltage setting seems to have nothing to do with the CPU, it affects not only the overclocking potential of the DDR3 SDRAM in your system. The same voltage is used for the memory controller that moved to the CPU from the chipset. It sets certain limits to the maximum possible setting for this parameter. Intel strongly advises that it shouldn’t be raised past 1.65V. Ignoring this warning may cause the frequency potential of the damaged CPU to go down permanently.
  • CPU PLL voltage (phase locked loop - a feedback control system that automatically adjusts the phase of a locally generated signal to match the phase of an input signal). This voltage used to be very important for successful overclocking of quad-core LGA775 processors, and is still important for overclocking Core i7. The nominal setting for this voltage is 1.8V, but Intel allows increasing it up to 1.88V without any risks for the processor.

As you know, increasing the voltage during overclocking makes the heat dissipation grow according to square-law. Therefore, when you overclock Core i7, as well as any other processors, it is important to monitor temperatures very carefully. Maximum allowed temperature for Core i7 is 100°C. If it heats up more, the CPU will enable thermal throttling, i.e. the Vcore and clock frequency multiplier will be forced down to 12x. This feature protects the processor die against dangerous overheating.

There are several different utilities out there that allow monitoring CPU temperatures, for example, CoreTemp or RealTemp. Using these utilities during stability tests of an overclocked processor will help find the optimal voltage setting for the overclocked CPU. They may also let you know if you need to improve your cooling.

However, it is important to keep in mind that Core i7 processors report only the temperatures of their computational cores, which allows to be more or less certain that these processor parts will not get overheated. At the same time, there is no way to control the temperature of the North Bridge built into the CPU. Besides, Core i7 has no integrated means of warning you about the overheating of the L3 cache and integrated memory controller, so you have to be extremely cautious when raising the Uncore and memory voltages.

 
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