CPU Overclocking Peculiarities

We started checking out the potential of EVGA X58 SLI Classified mainboard for processor overclocking as usual: with finding the maximum base frequency. It turned out that by lowering the memory frequency and reducing the processor clock frequency multiplier to 12, we could easily get the board to work at 215MHz base frequency. It is a very good result, this should be more than enough for our Core i7-920 processor sample and the mainboards inability to increase the base frequency high enough will not be a bottleneck in our case.

However, after the very first experiments we found out that the mainboard increases the voltages set in the BIOS quite noticeably under heavy load. Speaking of increased voltages, I mean not only the processor Vcore, although you can more or less deal with all other increased voltages by setting their values initially lower than desired. For example, when we set the memory voltage in the BIOS to the nominal value of 1.65V for our modules, it would increase to 1.72V. To avoid this excessive increase, we had to lower the initial setting to 1.6V. Maybe we should have set it even lower than that, because it would eventually increase to 1.66-1.68V during the tests. As for the processor core voltage, things are not as simple here, you shouldn’t really change it unless you absolutely have to. If you increase or even lower the processor Vcore, then on most mainboards Intel CPU power-saving technologies may partially stop working they way they should. It means that when the load reduces to minimum, only the clock frequency multiplier will be lowered, while the Vcore will remain the same, though too high for idle mode anyway.

This way, if you intend to overclock your processor but maintain the system power-efficiency, we should leave the processor Vcore at Auto in the mainboard BIOS. Under heavy load the current consumed by the CPU increases, while the voltage goes down and it is no longer enough for successful CPU overclocking. In this case we enable “EVGA VDroop Control” in the BIOS. This function shouldn’t increase the voltage but maintain it at the nominal level preventing from dropping. However, when we enabled “EVGA VDroop Control” on EVGA X58 SLI Classified mainboard, the processor Vcore went from the nominal 1.225V to 1.27-1.28V under heavy load. It is way too much.

Many mainboards from different manufacturers have something similar to “EVGA VDroop Control” in their BIOS. Everyone understands how dangerous it is to drop the processor Vcore under load. At some point it may lower too much and cause processor instability at the given clock frequency. That is why we are trying to prevent it from lowering. However, not everyone understands that increasing the Vcore is also harmful. You may think: we do increase the processor Vcore during overclocking in order to achieve higher clock frequencies, so what’s wrong about it? I believe I have to explain a few things.

The most obvious damage from raising the processor core voltage too high is the temperature increase. We set a specific value in the mainboard BIOS that is needed for stable work of our processor at the given frequency taking into account the utilized cooling solution. If the Vcore is increased, the cooler may no longer be efficient enough and we won’t be able to achieve maximum overclocking results. It seems that all we have to do in this case is to lower the processor core voltage by a certain value in advance, in order to avoid overheating. However, this is not a good way-out, because the core voltage doesn’t increase momentarily, it grows little by little that is why we may not have enough voltage in the beginning of our tests and again may fail to overclock our CPU fully. Moreover, the processor core voltage also depends on the load levels. I have seen multiple times how a CPU could successfully pass the long-term stability tests when all eight threads were busy, but would fail under small workload. In this case the Vcore doesn’t increase too much and hence is insufficient for stable operation.

Overall, overclocking results suffer when the voltage not only drops but also increases. The most optimal situation is when the board can maintain the core voltage at a certain level. Luckily, EVGA X58 SLI Classified knows how to do it. The processor Vcore is only increases significantly if it is set to Auto and “EVGA VDroop Control” function is enabled. However, if we set the processor Vcore at a certain specific value, the board stays on it pretty precisely. As a result, thanks to this feature as well as to overall excellent overclocking functionality of the EVGA X58 SLI Classified mainboard we managed to overclock our Intel Core i7-920 to 3.95GHz.

We have first achieved a similar result in early 2009 when we tested Gigabyte mainboards for Core i7 processors. Several months went by but none of the mainboards we tested afterwards could repeat this success. Now it has finally happened. EVGA X58 SLI Classified mainboard lowers the base frequency set in the BIOS by about 0.5MHz that is why we had to set it at 189MHz instead of 188MHz.

It is a great result, however when the processor Vcore changes Intel CPU power-saving technologies stop working on EVGA X58 SLI Classified, just like almost all other contemporary mainboards. It means that in idle mode only the processor clock frequency multiplier lowers, while the Vcore remains as is, at a relatively high level. It just doesn’t increase anymore.

Most mainboards we have tested so far could have the CPU working stably at 3.8GHz without increasing its Vcore and with the base frequency set at 181MHz. However, we were again luckier this time. EVGA X58 SLI Classified increased the processor core voltage in such a way that we could push the stability maximum a little further and overclock our CPU to 3.9GHz with the base frequency raised to 186MHz.

Under heavy load the CPU Vcore increased significantly, up to 1.28V. However, formally we overclocked without changing the CPU Vcore in the mainboard BIOS that is why all Intel processor power-saving technologies remained intact. Both: the processor clock frequency multiplier as well as the core voltage were lowered in idle mode.

It is very interesting that besides EVGA X58 SLI Classified, both recently tested mainboards – Foxconn BloodRAGE and DFI LanParty JR X58-T3H6 – also boasted the same “distinguishing feature”: they increased the CPU Vcore. However, they were not as good at it. Excessive Vcore increase wouldn’t let us overclock our processor to its maximum. As for overclocking without increasing the Vcore, it would be raised insufficiently to ensure stability at anything beyond the “standard” 3.8GHz.

Overall, we can conclude that although EVGA X58 SLI Classified does increase the processor Vcore under load, which is no good, it is done in such a smart way that it allows us not only to successfully overclock our processor to its maximum with the given cooling solution, but also to overclock it more without changing the core voltage in the BIOS. As you can see from the screenshots, the mainboard also allows raising the memory frequency to its maximum and setting the appropriate timings for it. As a result, we were very excited about the upcoming EVGA X58 SLI Classified performance tests in different operational modes.