We have also measured the power consumption of both graphics accelerators from the CrossFire system. Here we used a system based on Intel D925XCV Desktop Board, which was modified accordingly, so that we could measure the power on 12V and 3.3V lines of the PCI Express x16 slot. We also used a special adapter that allowed measuring the power send to the graphics accelerator via the 6-pin power connector. Our test system for this round of measurements looked as follows:
- Intel Pentium 4 560 CPU (3.60GHz, 1MB L2);
- Intel Desktop Board D925XCV mainboard;
- PC-4300 DDR2 SDRAM (2x512MB);
- Samsung SpinPoint SP1213C (Serial ATA-150, 8MB buffer);
- Microsoft Windows XP Pro SP2, DirectX 9.0c.
To create appropriate workload we ran FarCry 3D shooter Pier demo in 1600x1200 resolution with enabled FSAA and anisotropic filtering. When RADEON X850 XT CrossFire Edition is used as a single graphics card in the system, Compositing Engine doesn’t work. Therefore, the power consumption of this graphics accelerator remained the same as the power consumption of a regular RADEON X850 XT:
- RADEON X850 XT CrossFire Edition: 68.6W.
- RADEON X850 XT: 69.3W.
I doubt that the Compositing Engine requires more than 2-3W of power, so the difference in power consumption of the Master and Slave cards will anyway be negligible. Nevertheless, both cards working in a CrossFire system may consume up to 140W altogether. Of course, it is not so much compared with what two GeForce 6800 Ultra graphics cards would consume (155W), however it is a way higher than what a single GeForce 7800 GT would need (115W). ATI Technologies doesn’t recommend the use of any specific power supply units for CrossFire systems. However, keeping in mind our measurement results we would advise to go for high-quality PSUs with 400W+ capacity in continuous work mode. For example, a good choice in this case will be CoolerMaster RS-450-ACLY, Zalman ZM400B-APS or A.C. Ryan Ryanpower2 ACR-PS209. It would be best to avoid low-cost noname PSUs, because the specifications claimed on their stickers are very often different from the actual parameters. Besides, they are unreliable and do not guarantee stable output voltage because of too gravely simplified schematics.