Overclocking

Overclocking Core i7 processors is yet another “hot topic”. There are two questions that emerge here: how greatly the overclocking potential of the Core i7 processors differs from that of the previous generation CPUs, and how well the new platform architecture allows us to take advantage of this potential.

In fact, to answer these questions we performed a series of overclocking experiments with our Core i7-965 Extreme Edition processor. Unfortunately, at the time of the tests we didn’t have an alternative cooling solution available to us, so we had to stick to Intel’s default cooler. However, we hope it didn’t prevent us from revealing the frequency potential of the new processor properly.

Since the CPU we are going to experiment with belongs to Extreme Edition series, its multiplier is unlocked. It means that we may resort to the simplest overclocking technique.

So, without raising the processor voltage over its nominal 1.2V we could get it to run stably at 3.6GHz.

The CPU passed a 1-hour OCCT Perestroika 2.0.1 and Prime95 25.7 test at this speed. The core temperatures remained within acceptable range and never exceeded 78°C.

By the way, overclocking Core i7 by raising its multiplier is a little tricky at least on an Intel DX58SO mainboard. The thing is that this mainboard doesn’t allow increasing the multiplier above its nominal setting just like that. So, if you need to increase it, you have to use Turbo Boost technology: set high multipliers for turbo-modes at the same time pushing back the maximums for the current and power consumption. In other words, during overclocking we force the CPU to constantly work in turbo-mode by setting multipliers far beyond the nominal values.

Just like with the previous generation 45nm processors, increasing Vcore for Core i7 ensured its stability at higher frequencies. For example, by raising the core voltage of our CPU sample to 1.45V we could overclock it to 3.87GHz.

Unfortunately, our CPU lost its stability at 4GHz frequency, so we had to stick to the last operational frequency. Hopefully, when we check out new LGA1366 mainboards and high-performance coolers with the corresponding retention we will be able to improve our today’s achievement. At 3.87GHz when our processor was passing the stability tests it heated up to over 90°C. And it means that it was the cooling system that wouldn’t let us overclock any further. So, at this time we have to admit that new Core i7 so far overclock a little worse than their predecessors.

Now let’s address the second important question: will the owners of affordable non-Extreme Edition Core i7 processors be able to overclock their system too, even though they do not have the luxury of an unlocked clock multiplier? For the purity of the experiment we tried overclocking our Core i7-965 Extreme Edition by lowering its multiplier to 20x, because it is exactly the multiplier the youngest model in the lineup, Core i7-920 will have.

I am sure many of you will be pleased to hear that processor overclocking by raising host clock frequency went smoothly and problem free. I can even say that this processor is much easier to overclock than previous generation quad-core CPUs at least because Core i7 doesn’t require balancing the FSB voltage and CPU and chipset GTL levels, because this CPU doesn’t use the FSB bus. The most important thing to watch out for when you increase the clock generator frequency over the nominal 133MHz in an LGA1366 platform is the timely lowering of all multipliers setting the frequencies for different busses and internal units of the processor.

For example, when we lowered the multiplier for the memory frequency to 6x, for the integrated memory controller and L3 cache – to 12x, and for QPI bus – to 18x, we easily achieved system stability at 190MHz clock generator frequency.

The CPU frequency with the 20x clock multiplier was 3.8GHz. Unfortunately, we kept losing stability at higher clock generator frequencies and we couldn’t reach the same maximum as in the previous experiment when we used a higher clock multiplier. However, we tend to blame the early mainboard revision for this, and not some platform issues.