So, we managed to overclock our Core i7-920 processor to 181MHz base frequency without increasing its Vcore over the nominal value. The multiplier was raised to 21x thanks to enabled Turbo Boost, so the resulting CPU frequency equaled 3.8GHz. I think it is a very good result, because the CPU could process all 8 threads simultaneously under maximum load despite the low core voltage. No other voltages were increased, except the memory voltage. The only other thing we had to do to ensure stability was to enable “Load-Line Calibration” that prevents the processor Vcore from dropping under maximum workload.
The good thing about CPU overclocking without increasing its Vcore is that all processor power-saving technologies remain intact. As the load drops, they lower the clock multiplier as well as the core voltage.
I personally almost always overclock processors at their nominal Vcore settings and with all processor power-saving technologies up and running. However, not everyone shared this approach to overclocking. For example, it doesn’t make much sense to fight for power-saving if the CPU is loaded with work 24/7. It turned out that by simply increasing the processor Vcore to 1.3V, we could push the base frequency to 188MHz and hence the resulting CPU frequency – to 3.95GHz.
In this case the processor clock frequency multiplier will still be lowered I idle mode, but its core voltage will remain increased.
Unfortunately, I couldn’t get my CPU to work stably at a beautiful frequency of 4.0GHz even with its Vcore increased to 1.4V. I didn’t dare check out higher voltage settings because of extremely high core temperatures.
By the way, I am very surprised that some people claim Intel Core i7 processors overclock and remain stable at 1.4-1.45V Vcore. I wonder what type of cooling is used in this case? For example, when we overclocked our Intel Core i7-920 processor to 181MHz base frequency even without any voltage adjustments, its temperature increased to 76°C in Prime95 (the room temperature was around 22-23°C). 76°C is a pretty serious temperature, although I did use a highly efficient Cooler Master GeminII cooler with a 120-mm fan at 2500RPM inside Antec Skeleton system case, which is even better than an open testbed because it has an additional huge 250-mm fan at the top. Overclocking to 188MHz base frequency and 1.3V core voltage pushed the CPU temperature to 83-84°C. So, how much higher can you actually go?
Besides, a 120-mm fan rotating at 2500RPM becomes very noisy. This is actually why I replaced it with a quieter fan from the OCZ PSU. You can handle this noise for the time of tests, but it is hardly acceptable for long-term work.
As a result, I think that the only Core i7-920 overclocking that has any real practical value for us, is with the nominal core voltage settings. In this case we get more or less acceptable thermal characteristics and power-efficiency at an acceptable noise level. We lose all that the moment we raise the CPU Vcore, while the frequency increases just a little bit, by 150MHz, from 3.8GHz to 3.95GHz. I will try to back up my conclusions with a few benchmark results in the next chapter of this article.