Specifications
Once again, note that memory quantities are not added up in multi-GPU systems. The 2 GB found in quad SLI or quad CrossFire are really only 512 MB in practice. This is a serious limitation in high resolution, which by the way, is the target of such systems.
Power consumption
We evaluated the power consumption of the different systems. Measurements were taken at the wall socket, in order to have the total power consumption of the power supply, in this case a Cooler Master Real Power M1000 (1000 watt). Note that motherboards were different for AMD and Nvidia solutions; an Asus P5E3 (X38) and Asus Striker II (nForce 790i). The latter proved to generally consume a little less (roughly 10 watts).
The use of the 55 nanometer process and PowerPlay to reduce consumption, enabled Radeon HD 3870 based solutions to be relatively economical in stand-by. We say “relatively” because with a four GPU configuration, there is still an additional 100 watts that is being wasted. In load, PowerPlay no longer gives the Radeons this advantage.
The GeForce 8800 Ultras still show record consumption mostly in stand-by where readings are almost 100 watts per card. In load, a couple of Radeon HD 3870 X2s or GeForce 9800 GX2s show similar results.
Given that values come close to 700 watts for a "basic" system, in other words, without overclocking and multiple hard drives and other fans, it’s obvious that there will have to be a serious power supply.
Note that the GeForce 9800 GX2, alone or in Quad SLI, is
Hybrid Power compatible and can therefore be entirely turned off when used in a system compatible with this technology (such as the future nForce 780a for AMD processors). We will have to wait for summer until a similar alternative arrives for the Core 2.
The test
For this test, we used ten games, four of which support DirectX 10. Tests were carried out in 1920x1200 and 2560x1600, the resolution of 30" screens.
Anisotropic filtering as well as HDR were activated in all cases when available in the game. Finally, transparency/adaptive antialiasing were activated in multi-sampling mode.
Of course, all Windows Vista updates relative to performance and multi-GPU systems were installed.
Configuration
Intel Core 2GB Extreme QX9770
Asus Striker II nForce 790i (GeForce)
Asus P5E3 X38 (Radeon)
2 GB DDR3
Windows Vista
Forceware 174.53
Catalyst 8.3
