Intel's Core i7 processors are equipped with integrated circuits, which are meant to protect the CPU from overheating or from excessive electric currents (TDP/TDC settings). However, the thresholds for these features, which effectively are limiters, throttling the processor clock speed and voltage when the threshold is reached, can be altered in the BIOS if the processor Turbo mode is activated. Now it is possible to set higher clock speeds and voltages to reach better performance on liquid nitrogen cooling.

EIST Attacks From Behind

Unfortunately, Turbo mode requires Intel's Enhanced Speedstep feature (EIST), which is responsible for automatically adjusting multipliers in an effort to reduce idle power consumption - or to run a single core at two multipliers above the specified speed. The reason behind the Turbo mode to accelerate single threaded applications, which run faster on higher clock speeds.

The issue with EIST is that it would still drop the voltage when the system runs idle, even though the multipliers aren't changed. Still, insufficient voltage is a huge issues for our overclockers, who have been running Core i7 at 4.7 to 5.1 GHz - this requires voltages of approximately 1.5 V.

How Turbo Mode Can Have The Reverse Effect

Once the Turbo mode is activated, it is also important to make sure that the TDP (Thermal Design Power) and TDC (Thermal Design Current) limits are set to the maximum value, as the feature cannot be disabled. Once taken care of, the processor would not throttle when it reaches its current or power maximum, which was specified at 130 W. The system will remind you to take care of the TDP and TDC values once you set a high multiplier like e.g. x28, and run a benchmark that has all cores operate at peak power. In such a case, the protective mechanisms willautomatically utilize the EIST feature to drop two multipliers in an effort to protect the CPU.

Team IronMods says that there definitely are ways to ignore the TDP/TDC readings and lock in the multiplier for good. Unfortunately, not all motherboard makers managed to implement this yet.

Source : Tom's Hardware US