Overclocking Core i7: Power Versus Performance

Overclocking Choices And Details

We used the following settings to overclock our Core i7 920. Most of the selected voltages were necessary to successfully and reliably overclock the processor to 3.8 and 4.0 GHz. Speeds faster than 4.0 GHz were not reliable on several air coolers, but we know that they can be achieved if you're willing to spend more on cooling.

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Clock Speed Voltage133 MHz150 MHz166 MHz183 MHz190 MHz200 MHz
CPU Clock2.67 GHz3 GHz3.33 GHz3.66 GHz3.8 GHz4 GHz
CPU VoltageAutoAutoAuto1275 V1.344 V1.5 V
GPLAutoAutoAuto1.8 V1.94 V2.1 V
QPI/DRAM VoltageAutoAutoAuto1.275 V1.344 V1.5 V
DRAM VoltageAutoAutoAuto1.6 V1.6 V1.6 V

Core i7 Turbo Mode

Turbo Mode is available on all Core i7 processors; it allows the processor to accelerate one core by one or two multiplier increments (133 MHz or 266 MHz at stock speed) when fast single-thread performance is required. We left this mode enabled at the settings up to 3.33 GHz (3.314 MHz), as it introduces a further clock speed increase of 169 MHz (equivalent to one multiplier at increased QuickPath Interconnect base clock) without requiring a voltage increase.

Overspeed Protection

At 4 GHz we observed that Intel’s overspeed protection kicked in. The primary purpose of this feature is to protect the processor from overheating at highly overclocked settings by effectively throttling the processor speed. The feature could not be switched off with the BIOS version we used, and it kicked in when we set the system to run at 4.0 GHz. Its activation became obvious as we observed performance that was actually not much superior to that at the 3.8 GHz setting, and also by the system power consumption: while we initially measured a 417 W peak power, this number fell to 370 W after a few minutes of operation, showing that the CPU was throttling. CPU-Z confirmed the results.

It is typically possible to delay the overspeed protection kicking in by applying more powerful cooling products such as a liquid cooling solution. Since the focus of this article is reasonable overclocking, though, we decided to stick with the stock cooler from Intel (although it’s certainly not the best choice for serious overclocking).