We perform our power consumption measurements with an Extech Power Analyzer 380803. This device is connected before the PSU and measures the power draw of the entire system (without the monitor), including the power loss that occurs on the PSU itself. In the idle mode we start the computer up and wait until it stops accessing the system drive. The mainboards are sorted in the order of ascending power consumption. The results of the ASUS Z97-A are colored differently for the sake of readability.
The difference between the mainboards is obvious now. The ASUS Z87-PLUS needs more power. Well, neither mainboard uses optimal settings by default, so let’s see what we have after we enable all of their CPU-related power-saving technologies.
Our configurations need less power now, yet the ASUS Z97-A is still more economical. It's hard to explain this result. The Z97 and Z87 chipsets are specified to have the same power draw of 4.1 watts. The mainboards both have 8-phase power systems. The Z87-PLUS has an additional SATA controller, but it can't account for such a big difference. There must be several factors contributing to it.
We want to remind you that we install an AMD Radeon HD 7970 graphics card into our test configurations. If we instead used the CPU-integrated graphics core, the overall power draw would be lower than 30 watts. Haswell-based CPUs are indeed very economical when idle, so it is a shame that the mainboards do not ensure this advantage by default. You have to correct some BIOS options for that.
For power consumption tests under high load we run the LinX 0.6.4 utility, which is a graphics shell for Intel’s Linpack test and supports AVX instructions. It is heavier on the CPU than ordinary applications, yet it is just an application nonetheless. It is quite possible that there are some other programs that can be just as heavy. That’s why we stick to using LinX for the purpose of checking the computer out for stability and for measuring its power consumption.
Both mainboards need 118 watts at this load, but the number doesn't reflect the typical power draw of LGA1150 products. These ASUS models drop their CPU clock rate at high load, so they consume less power but perform slower. The normal level of power consumption is somewhere above 130 watts. We'll see such numbers in our upcoming reviews of mainboards from other brands. However, if you manually increase the CPU power targets in the BIOS, even these mainboards from ASUS will become normal: they’ll consume more power and deliver higher performance.
Now let’s see how much power the mainboards need in idle mode when overclocked. We always use as many power-saving technologies as possible while overclocking. That’s why the standings are the same as at the default settings. The mainboards need 1 watt more compared to the Eco settings. However, both mainboards need less power when overclocked with increased voltage than at their default, non-optimized settings (see the first diagram). So, do not leave the settings at their defaults. You should explicitly enable all CPU-related power-saving technologies even if you don’t overclock your CPU.
By the way, you have to count in the graphics card’s power draw at high loads to calculate the overall system consumption. We use high CPU loads in our power consumption tests, but if we load the AMD Radeon HD 7970 by running some heavy game, the total power draw will be close to 250 watts at default settings and even higher at overclocking.
It is only in idle mode that the mainboards differ. They consume the same amount of power at high loads.