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That’s all we can tell you about overclocking Haswell-based CPUs on different mainboards in the energy-efficient way, i.e. without any volt-modding. Now you only have to increase your CPU frequency multiplier, looking for the highest clock rate the CPU is stable at. Most likely, it will be in a range of 4.0 to 4.3 GHz. There are a lot of special tools that can help you test your computer’s stability. The LinX utility, a graphics shell for the Intel Linpack test, creates a very high load, but serves better for testing CPU coolers rather than stability. If it produces errors, the CPU is overclocked too much. So LinX is good for preliminary testing whereas Prime95 is appropriate for a final check. In fact, you can use any utility that creates high load or the specific load your computer is supposed to cope with. If the computer passes the test successfully, you increase the CPU clock rate further and vice versa. Eventually you will find the peak frequency your CPU can work at continuously - just don’t forget to monitor its temperature, too.

Although such energy-efficient overclocking is optimal and suitable for nearly every user, sometimes you may want to get the maximum frequency possible at all, regardless of power consumption and other factors. In this case, you have to increase your CPU voltage to ensure stability and high clock rates. We used to increase voltage in the offset mode and the LGA1150 CPUs also support a similar adaptive mode, but such methods do not work well with Haswell-based CPUs. The fact is as soon as the default voltage is changed even by a tiny value, the Haswell’s integrated regulator will spot it and increase the voltage further at high loads, which means high heat dissipation, high temperature and, eventually, overheat. To avoid this, the Haswell must be overclocked at a constant voltage. The downside is that the CPU’s power-saving technologies cease to work: the CPU frequency multiplier drops at low loads but the voltage doesn’t drop anymore and always remains at the constant and high level. This is the only way to deal with the integrated voltage regulator, though. Moreover, it doesn’t affect the computer’s power draw in idle mode.

As an example, we can show you a diagram that helps compare different mainboards in terms of their power consumption at zero load. There are three test modes: 1) standard settings, 2) the CPU is overclocked to 4.5 GHz, the voltage is increased to 1.150 volts, and the memory is overclocked from 1333 to 2133 MHz, 3) Eco mode which is the same as the standard settings but the power-saving options are manually switched from Auto to Enabled (as described in the previous section of this article). Thus, you can see how much power each mainboard needs at different settings. The results are quite paradoxical. When overclocked, our configurations need about as much power as in the eco mode, which is the effect of enabled power-saving technologies. It is at the default settings that the power consumption is at its peak. It proves that you have to enable each and every power-saving feature to make sure that your computer is energy efficient.

Of course, the diagram only refers to the computer’s idle state. It’s different when there is some load. For example, we’ve got a rather good sample of the Intel Core i5-4670K processor. At the default voltage it can be overclocked to 4.3 GHz. And if the voltage is increased to 1.150 volts, it is capable of working at 4.5 GHz. Overclocking from the default 3.6-3.8 GHz to 4.3 GHz means a substantial performance boost whereas the additional overclocking by 200 MHz translates into a 5% performance increase in computing tasks while the power consumption grows up by 40%. The power draw will get even higher if the voltage is increased more. That’s hardly efficient and rational since the temperature grows up, too. There is also more noise from the CPU and PSU fans. That’s why we recommend overclocking without increasing voltages: the power consumption, temperature and noise do not change much then.

Overclocking with volt-modding is done in the same way as without volt-modding. You increase the clock rate as long as the computer passes stability tests. The only difference is that if the CPU can’t work at a given clock rate, you help it by increasing its voltage. To what level exactly? Check out which voltage is reported by your monitoring utility at standard settings and set it somewhat higher. You will probably start from 1.120-1.130 volts and move on in small steps like 0.010 volts. Make sure the temperature doesn’t get too high, especially above 90°C. Some tests can be carried out at very high temperature but the CPU will enable thermal throttling, which leads to a performance hit. In this case, you may even find your overclocked computer to be slower than at the default settings.

You will see that each next overclocking step requires more and more voltage. So when your CPU cannot pass a stability check and doesn’t react to your increasing its voltage, or if its temperature gets too high, you should go back to the previous clock rate and set the lowest voltage necessary for it. Once again run your stability tests and then proceed to overclock your system memory and graphics card.

There is one more thing you should be aware of. The voltage on the CPU cores is usually the only voltage that affects stability of an LGA1150 platform. However, when it is set very high, you may find it necessary to increase the CPU input voltage as well. At its default level of 1.8 volts it is enough to let you increase your CPU voltage to 1.3-1.35 volts. You will only need to adjust the CPU input voltage if you’ve got a special CPU cooler. With ordinary cooling solutions and non-modified CPUs, it is better to remain within 1.2 volts.

We haven’t touched upon some points regarding Haswell-based CPUs because the article is quite long as it is. For example, the cache memory frequency may also be tweaked. Theoretically, it is better to set it as high as possible, but in most cases this factor doesn’t affect performance and should be left for the mainboard to set up. Then, CPUs can also be overclocked by increasing the base clock rate along with the frequency multiplier. This method doesn’t provide any significant benefits, yet you may want to try it if you feel like experimenting.

 
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