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CPU Overclocking Details

ASUS mainboards do not provide any hotkey prompts and do not report the CPU clock rate correctly when starting up. They make it difficult to enter their BIOS interface and don’t enable all of the available power-saving technologies by default. They also do not ensure the standard operation mode for the CPU at high loads. That’s not an inspiring start for our tests of the ASUS Z87-Deluxe. And, as a matter of fact, we expected to find more problems as we tried to overclock the mainboard.

In our ASUS Z87-K review we told you about two methods of automatic CPU overclocking: Ratio Only and BCLK First. There are three ways to enable such overclocking: OC Tuner (in the BIOS), 4-Way Optimization (from AI Suite III), and the onboard TPU switch. In the Ratio Only mode the CPU is overclocked by increasing its frequency multiplier whereas in the BCLK First mode the base clock rate is increased as well. Any automatic overclocking is imperfect, though. You can always do better by doing everything manually and gain advantages in terms of frequency or power consumption. We had no doubts the Z87-Deluxe was going to overclock well since the simpler ASUS Z87-K had overclocked our CPU without any problems before. And the top-end model has a more advanced power system and more flexible setup options. There was one hitch, though.

The ASUS Z87-K was the first LGA1150 mainboard we used to test Haswell-based CPUs. The Haswell’s integrated voltage regulator increases voltage too much in overclocked mode at high loads. To prevent this, we had to fix the voltage at a certain level. In this case, some of the CPU’s power-saving features stop to work: the CPU’s multiplier is lowered at low loads but the voltage doesn’t drop. Other ways of increasing the voltage (in the offset or adaptive mode) were no good because the integrated regulator would set the voltage too high at high loads. We had even suspected that this effect accompanied any overclocking, but it turned out to be only due to increased voltage rather than increased frequency. The Gigabyte GA-Z87-D3H helped us realize this fact and the frequency of 4.3 GHz was quite good for an Intel Core i5-4670K.

It is extremely easy to overclock Haswell-based CPUs in an energy-efficient way on Gigabyte mainboards. You only have to fix the voltage at a certain value and increase the clock rate to the desired level. As we tested mainboards from other brands, we found that ASRock, Intel and MSI products could be overclocked in the same way as well, with some reservations. ASUS mainboards, on the contrary, would increase the CPU voltage as soon as you increase the voltage. This is a long-time feature and its purpose can be easily explained. Mainboards from other brands will not be able to start up if an inexperienced user increases the CPU frequency but doesn’t increase the voltage whereas the ASUS mainboard will start up by automatically increasing the latter. This feature interfered with our overclocking in the past but we could bypass it by increasing the voltage by 0.001 volts. This doesn’t affect the behavior of any CPUs except for the Haswell, though. The Haswell’s integrated voltage regulator notices this difference and increases voltage to extremely high levels and high loads. And if we don’t increase the voltage ourselves, the mainboard does that as soon as we raise the CPU frequency.

Fortunately, ASUS has reacted to the new situation quickly. The ASUS Z87-Deluxe adjusts CPU voltage in a different way. If the CPU clock rate is increased, but the CPU Core Voltage option is Auto, everything remains as before: the voltage will be increased automatically. In our case, with an Intel Core i5-4670K processor and a frequency multiplier of x43, the voltage would peak up to 1.224 volts even at moderate loads. This is already too high. At high loads, the voltage would go up to 1.3 volts and higher, provoking overheat. So, to avoid this, you have to change CPU Core Voltage to Manual. In this case, the mainboard and the integrated regulator don’t increase the voltage anymore, so the latter remains at 1.135 volts even at high loads on our CPU overclocked to 4.3 GHz – just like on the other mainboards we tested.

Energy efficient overclocking is only possible if you don’t increase voltage. It will ensure higher performance and, despite the increased power consumption, you can expect long-term savings due to the reduced amount of energy spent for each computation. Energy efficient overclocking is going to be environment-friendly as we showed in our Power Consumption of Overclocked CPUs review. However, when we test mainboards, we want to check them out under different conditions and loads, so we choose what overclocking method ensures the highest results. Higher clock rates and voltages mean harsher test conditions and it is under such conditions that we can better see any flaws or problems in mainboard design. That’s why we overclock our CPU to 4.5 GHz in our mainboard reviews, fixing the voltage at 1.150 volts and using the XMP settings for our memory modules.

When we overclock by fixing the CPU voltage at a certain level, some of the power-saving technologies get disabled. The CPU's frequency multiplier is lowered at low loads but its voltage always remains high. Anyway, we stick to this overclocking for the duration of our tests, especially as it doesn't affect the computer's idle power draw much.

The overclocking results seem to be the same as with the other mainboards, but the CPUID screen from AIDA64 doesn’t show one important parameter – the clock rate of the CPU’s L3 cache. Haswell-based CPUs have a dedicated multiplier for the clock rate of the ring bus, which is also the clock rate of the L3 cache and memory controller. Although the cache clock rate can be set up independently, it equals the CPU’s clock rate with each tested mainboard. When our Intel Core i5-4670K works in its default mode, the cache memory frequency varies dynamically in a range of 800 MHz to 3.8 GHz. The same is true for the ASUS Z87-Deluxe. However, when the CPU is overclocked, the cache memory frequency doesn’t change anymore. It becomes constant at 3.8 GHz whereas on the other mainboards it drops to 800 MHz in idle mode and goes up to 4.5 GHz at high loads, in sync with the CPU clock rate. We carried out some tests and made sure that, despite the difference, the cache memory frequency didn’t affect the performance of the mainboard in most applications except for archiving. The ASUS Z87-K was slow with the WinRAR archiver, both at its default setting and in the overclocked mode. Let’s see what we have with the ASUS Z87-Deluxe but, to make our performance tests accurate, we manually set the frequency range of 800 MHz to 4.5 GHz for the cache memory.

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