Energy consumption and efficiency For the energy consumption analysis we tried to use a test which is more or less representative for all architectures of what we get in applications in terms of performance and energy consumption. In the end we opted for Fritz Chess Benchmark once again. In addition this application has the advantage of allowing us to fix the number of threads to be used.
The energy consumption readings therefore shouldn't be taken as absolute maximum values but rather as typical of a heavy load - applications specialised in processor stress such as Prime95 can consume up to 20% more. All energy economy features, including those on motherboards such as the ASUS EPU, were turned on for this test, as long as they didn't have a negative impact on performance.
Remember we give two types of readings, the first at the 220V wall socket using a wattmeter for the whole test configuration and the second at the ATX12V via a clip-on ammeter. This reading allows us more or less to isolate the energy consumption of the processor but it isn’t unfortunately exactly comparable from one platform to another as in some cases a small part of the CPU energy consumption comes from the standard ATX 24 pin socket.
Note that in comparison to the Intel DP67BG motherboard used previously for LGA 1155, the Intel DZ77GA-70K is very uneconomical in its current state, at idle first of all with an energy consumption increase of 15 Watts at the socket and 4.8 Watts at the ATX12V, which seems to be because of the numerous additional chips and the poor efficiency of its power stage at idle. Note, when at idle, going by the LEDs on the motherboard, one phase remains on and the others aren’t completely off either as their LEDs flicker. However optimal yield at idle is supposed to be obtained with a single active phase.
In load there’s also quite a difference, notably due to a lower Vdrop impact, with the Core i7-2600K 17 Watts higher at the socket and 9.6 Watts higher at the ATX12V and the i5-2500K 16 and 7.2 Watts higher. We have therefore given the values obtained on each of the platforms, the other Sandy Bridges only being measured on P67 and the Ivy Bridges only on Z77, which allows us to compare the Ivy Bridges between each other .
[ 220V socket ] [ ATX12V ]
The energy consumption taken at idle is similar between the Core i5-2500K and i7-2600K models and the i5-3570K and i7-3770K, with however something rather strange happening linked to the DZ77GA-70K motherboard. If we look at the numbers obtained on this board, we can see that there’s a smaller gain with a single thread: with the i5s we’re down from 25.2 to 24W at the ATX12V and from 28.8 to 25.2W with the i7s.
When the processor is occupied at 100%, the gap grows with the i5s dropping from 60 Watts on Sandy Bridge to 51.6 Watts on Ivy Bridge and the i7s dropping from 73.2 to 64.8 Watts. This represents respective energy consumption reductions of 14% and 11.5%.
We therefore chose to use two different methods to isolate the processor energy consumption:
- Energy consumption at the ATX12V
- 90% of the difference in energy consumption between load and idle at the socket
We took this at 90% so as to exclude power supply yield. Note that while the first reading favours processors that draw a small proportion of power from the standard ATX socket, the second favours those with high energy consumption at idle. Unfortunately no method is perfect.
[ 220V socket ] [ ATX12V ]
With the DZ77GA-70K the energy efficiency of processors on the ATX12V has gone down, which was to be expected given the fact that the energy consumption is higher than with the DP67BG. At maximum load and with an identical motherboard, Ivy Bridge gives a gain of about 20% (20.8% and 19.2% on i5 and i7 at 90% of the difference at the socket, 23.7% and 19.9% at the ATX12V), but it should be noted that Fritz doesn't really benefit from the Ivy Bridge IPC improvements as we'll see in the tests at equal clocks.