The Phenom II X4 940
For this test, AMD supplied us with a Phenom II X4 940 clocked at 3 GHz. The first surprise is that it has a voltage of 1.35V as against 1.3V for our Phenom X4 9950. So AMD hasn’t been able to reduce the voltage in spite of finer engraving, which would normally limit any energy consumption gain.
Energy consumption
We begin measuring processor energy comsumption at the ATX12V socket. Note that because of the different power supply systems of these processors, the memory controller that is not integrated on the Core 2 and which consumes 10 to 15W in load is included in the scores for the Athlons and the Phenoms, but not on the Core i7 (same for the L3), the “uncore” part being supplied from the ATX standard socket.
Energy consumption at rest has fallen significantly, from 17W for the largest Phenom to 11.2W for the largest Phenom II. Note that the Cool’n’Quiet has been improved, the Phenom running at 1.3 GHz at rest at 1.05V and the Phenom II running at 800 MHz at 1V. Without Cool’n’Quiet the Phenom II is at 31.6W against 29.3W for the Phenom.
There is also an improvement in performances with Cool’n’Quiet activated. With the Phenom, activation of Cool’n’Quiet sometimes brings a significant drop in performance. This is no longer the case with the Phenom II.
In load there is a much better ratio when only 2 cores are used; the Phenom consumes 45% more energy. The difference is down to 27.5% in full load. Compared to the Core 2s, the Phenom II uses more energy, even if you take into account the integrated memory controller. Note that Intel sent us a Q9400S a few weeks ago. The Q9400S has a TDP of 65W rather than 95W for the Q9400: in practice we didn’t actually notice much difference between the processors… indeed the TDP of 95W was significantly overestimated.
When you look at the configurations as a whole at rest, the lowest energy consumption is with the AMD combo 790GX/Athlon X2 6000 which is 11w more economical than the P45/Pentium E5300 combo, but in load the Intel advantage is huge at 42w less than AMD.
This platform level economy gives the Phenom II configuration an overall consumption at rest that is between what you get with a Q8300 and a Q9300. In load however it’s another story as the Phenom II is at the same level as the QX9770, or 36w more than a Q9400. The Core i7 platform gives a better level of performance … but also consumes the most energy, above all when the whole processor is being used with 8x Prime (as a result of hyperthreading).
Overclocking
As you saw in the introduction, AMD increased the frequency of the Phenom IIs in comparison to the Phenom when it moved to the 45nm engraving process, something it didn’t manage when moving to 65 nm and 90 nm. Not satisfied with this gain, AMD is also vaunting the overclocking capacities of these Phenom IIs and says that with good air-cooling you can generally achieve 3.65 to 3.90 GHz at between 1.4 and 1.55 V.
On our test processor, clocked at 3 GHz and cooled with a Noctua NH-U9B, we got up to 3.4 GHz while staying at 1.35V. An extra 0.1V allowed us to stabilize the clock at 3.6 GHz and we had to push up to 1.55V to get a clock of 3.7 GHz. At these settings, energy consumption goes up to 117.6W… or the equivalent of that of a Phenom X4 9950 that is not overclocked!
Of course we’ll have to see what the processors on general sale give to find out exactly what the Phenom II does in terms of overclocking, but it seems as if results should be good at reasonable voltages. The problem of course lies in defining what a reasonable voltage is, with exact datasheets not yet available on the Phenom II. In its specs AMD speaks about a nominal voltage of between 0.875 and 1.5V, but by default AMD OverDrive won’t allow voltage to go beyond 1.45V. What voltage burns the processor out? AMD doesn’t say, in contrast to Intel who, for example, say that the 65 nm Core 2s can go up to 1.55V as against 1.45V for 45 nm versions.
The fact that this information is not given is that much more of a shame as the Phenom II would seem to respond pretty well to increases in voltage, allowing overclockers to push up to 5 or 6 GHz with perhaps 2V if you really want to go for it!
