We measured power consumption using Extech Power Analyzer 380803 device. This device was connected before the system PSU, i.e. it measured the power consumption of the entire system without the monitor, including the power losses that occur in the PSU itself. When we took the power readings in idle mode, the system was completely idle: there were even no requests sent to the hard drive at that time. We used LinX program to load the Intel Core i3-540 CPU. For more illustrative picture we created graphs showing the power consumption growth depending on the increase in CPU utilization as the number of active computational threads in LinX changed in nominal mode as well as during overclocking. The boards are sorted out in alphabetical order on the diagrams below.
In nominal mode Gigabyte mainboard appeared more energy-efficient. It is quite logical, since Asus P7H57D-V EVO is larger, more complex and uses more additional onboard controllers than the small Gigabyte GA-P55M-UD4. This overall picture repeats also during processor and memory overclocking, only under maximum load the boards’ power consumption readings are about the same, which is also not surprising. To overclock the processor higher on Gigabyte mainboard we had to increase CPU Vcore a little more, which resulted into a noticeable increase in power consumption. There is another thing that seems pretty paradoxical here: in idle mode when the CPU is overclocked by raising the processor core voltage, Gigabyte solution turns out more economical than in the nominal mode: this system consumes only 71 W instead of 81 W!
It may seem unreal and contradicting the laws of logics, but the explanation is again connected with the notorious “Auto” settings. It turned out that both mainboards allow the CPU to switch to deeper power-saving modes in idle state, when the corresponding BIOS settings (“C State package limit setting” on Asus and “C3/C6/C7 State Support” on Gigabyte) remain set to Auto. We didn’t change anything in the nominal mode, but during CPU overclocking we explicitly indicated for Gigabyte mainboard that it should keep all processor power-saving technologies up and running by setting all parameters in the “Advanced CPU Core Features” section to “Enabled” instead of “Auto”. By the way, if you set “C State package limit setting” parameter on Asus mainboard to “C6” instead of “Auto”, the mainboard will consume considerably less power in idle mode: this reading will drop to approximately 81 W in nominal mod and 91 W in overclocked mode. As a result, you will save a lot of power, especially considering that the CPU is mostly idle during common everyday computer work.