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). We added the results of a system equipped with a single Radeon HD 3870 but based on an nForce 680i platform like all the GeForce cards in order to have an idea of the difference in consumption related to the motherboard and chipset.
The use of the 55 nanometer process and PowerPlay to reduce consumption enabled the Radeon HD 3870 to be very economical in stand-by. It’s an entirely different situation for the GeForce 8800 Ultras which use quite a bit of energy. A single one requires more power than two GeForce 8800 GTs!
While the GeForce 8800 Ultra measurements in load could be acceptable because it is a very high end system, at rest the amount is more problematic. Each one of its cards uses almost 100 watts or 300 watts in total uselessly wasted by the whole configuration.
Either way, you will have to make sure that you have an adequate power supply to use such systems.
Set up
Activating SLI or CrossFire in drivers is very simple as you only have to check a box in their specific panel. Both AMD and Nvidia integrate a hardware and software version of their multi-GPU technology. The hardware version uses dedicated components present in GPUs as well as the specific connector to transfer information (or at least the biggest possible part of it) from one card to another. This is the highest performance mode. The software version works with the PCI Express bus to transfer all the data between cards and is therefore a little less efficient.
CrossFire and 3-way SLI connections.Of course, we used the hardware version in all cases. For CrossFire, two connectors are currently required, one in each direction; however, AMD told us that in the future only one would be necessary. For Nvidia, a single connector is needed for SLI while a special one is needed for triple SLI which allows interconnecting all cards (the 1st to the 2nd, the 2nd to the 3rd and the 3rd to the 1st). It’s something that doesn’t come with nForce 680i motherboards and has to be acquired while NForce 780i motherboards include it with their bundle.
Note that for SLI, Nvidia also authorizes the software version. This isn’t the case for CrossFire with two Radeon HD 3870s or triple SLI which can only be activated once the special connector is in place.
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 multisampling mode.
Of course, all Windows Vista updates relative to performance and multi-GPU systems were installed.
Configuration
Intel Core 2 Extreme QX6850
eVGA nForce 680i SLI (GeForce)
Asus P5E (Radeon)
2 GB DDR2
Windows Vista
Forceware 169.04 (169.28b for Crysis)
Catalyst 8.1 hotfix.
