We performed our power consumption measurements using the same 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 in the PSU itself. In the idle mode we start the system up and wait until it stops accessing the hard disk. The power consumption in case of single-threaded CPU load is measured while running the Pi-digits performance test, and in case of multi-threaded load – while running the Fritz Chess Benchmark test. We didn’t analyze the power consumption under complex load this time. If there is a powerful discrete graphics card in the system, it does affect the overall total system power consumption, and this additional factor must be taken into account. However, things were completely different with the integrated graphics core. Contemporary games rarely use multiple CPU cores, usually involving only one or two at the most. Therefore, even with integrated graphics the power consumption in games is lower than in case of 100% CPU utilization, although it is still higher than in case of a single-threaded load. The results on the diagrams are sorted out in ascending order for your convenience.
Intel’s power-saving technologies that reduce the CPU frequency multiplier and voltage at low loads are all active on both mainboards by default but the Gigabyte GA-Z77M-D3H looks preferable in terms of idle power consumption. The ASUS P8Z77-M, in its turn, is more economical at high loads. It must also be noted that you can achieve more economy with ASUS mainboards at any loads by enabling EPU Power Saving Mode in the BIOS. Gigabyte mainboards lack a feature like that.
Now let’s compare these configurations with the CPU and memory overclocked.
The Gigabyte GA-Z77M-D3H is more economical in every mode, which is the consequence of its lower overclocking potential. It didn't let us increase voltages, so we couldn't overclock our CPU well enough. The ASUS P8Z77-M needs more power just because the CPU works at a higher clock rate. The increased performance justifies the higher power consumption.