Socket Compatibility and Power Consumption

Socket Compatibility explained: AM2+ and AM3

We keep repeating this tidbit in our Phenom processor reviews. But we feel it is imperative to explain. AMD has an approach we here at Guru3D like to see very much. That is try to stick as long as they can with a processor socket design. Therefore the good news is, even if you have an AMD 790 AM2+ compatible motherboard, you can pop in the new AM3 processors and it'll work.

Mind you that if you do so, and this is a very strong recommendation, upgrade your BIOS (motherboard BIOS) before upgrading to the new processor, to gain the latest Phenom II compatibility straight out of the box. Motherboards wise any AMD 790 FX or GX chipset purchased last year should be compatible with Socket AM3 processors. Some of you might even have luck with slightly older AMD 780 chipset based motherboards. But for 780 motherboards there is a second restriction, please do make sure your motherboard can handle the power requirements of the processor. Please check this with your motherboard manufacturer.

What is the big deal about Socket AM3 then?

Socket AM3 based motherboards are introduced with merely one thing in mind, to get DDR3 memory support.

Today's processors reviewed are in fact Socket AM3 processors. So (and again to make it clear) it will fit fine on Socket AM2+ motherboards which do support Phenom II. The only snag is that you are forced to use DDR2 memory, though the performance hit really is marginal.

What's the physical difference in-between the two sockets ?

Two extra pins (940 for AM2+ vs 938 for AM3) makes the older chips mechanically incompatible with the new socket, preventing users from attempting to install an old chip in a new board.
So if you want to go for DDR3, a migration towards an Socket AM3 motherboard is mandatory. Once you do have a Socket AM3 motherboard, you'll get support for up-to DDR 1333 MHz memory. On socket AM2+ you'll be able to make use of DDR2-1066 MHz memory, while on socket AM2 you'll be limited towards 800 MHz.

Power Consumption

The new AM3 Phenom II X4 processors announced today have a pretty good TDP (peak wattage), compared to the last flagship products they shaved off 20 watts while increasing performance. The tested Phenom II X4 945 and 955BE processor has a TDP of 125 Watt (= 125W peak, when all 4 cores in the processor are 100% utilized and stressed).
Much like the last-gen products, we have four active & independent cores here. Each core can be clocked down independently if not utilized, saving heaps of current. If the processors are temporarily inactive, they can pretty much put themselves in sleep-mode (clocking down). Hyper Transport will power down and a low-power stage is activated on the memory.

AMD's Cool'n'Quiet technology was recently updated to revision 3.0 and provides even better power management. Keywords here are improved power tuning with additional performance states, and up to 50% less power at idle compared to Cool'nQuiet 2.0

As a result we notice our test platform peak out at roughly 180 Watts power consumption when we stress the CPU cores. Our system however idles merely at 129 Watts (dedicated graphics processor used, not a integrated one).

Now since we used an 790FX based AM3 motherboard we had to add a dedicated graphics card (GTX 280), you'll notice that the end-result overall in idle and peak wattage is very impressive. Small note, the 810 and 940 results shown did not have a dedicated graphics card installed, yet used the GPU inside the 790GX chipset.

As you can see once we stress four CPU cores with Prime95 (stress test), our power consumption maxes out at ~180 Watts. Not bad man.