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Test notes
CrossFire X presents a wealth of possible test configs, but we chose a couple that we thought would be representative of common configurations. For our quad-GPU tests, we used a pair of Radeon HD 3870 X2 cards, and for three GPUs, we used a single Radeon HD 3870 X2 paired with a Radeon HD 3870. Our test motherboard, a Gigabyte GA-X38-DQ6, has two PCIe x16 slots with a full 16 lanes of PCIe 2.0 connectivity routed to each. These hardware combinations should be more or less optimal for CrossFire X in terms of interconnect bandwidth and the like, giving it plenty of opportunity for performance scaling.

Please note that we tested the single and dual-GPU Radeon configs with the Catalyst 8.2 drivers, simply because we didn't have enough time to re-test everything with Cat 8.3. The one exception is Crysis, where we tested single- and dual-GPU Radeons with AMD's 8.451-2-080123a drivers, which include many of the same application-specific tweaks that the final Catalyst 8.3 drivers do.

Our testing methods
As ever, we did our best to deliver clean benchmark numbers. Tests were run at least three times, and the results were averaged.

Our test systems were configured like so:

Processor Core 2 Extreme X6800 2.93GHz Core 2 Extreme X6800 2.93GHz
System bus 1066MHz (266MHz quad-pumped) 1066MHz (266MHz quad-pumped)
Motherboard Gigabyte GA-X38-DQ6 XFX nForce 680i SLI
BIOS revision F7 P31
North bridge X38 MCH nForce 680i SLI SPP
South bridge ICH9R nForce 680i SLI MCP
Chipset drivers INF update 8.3.1.1009
Matrix Storage Manager 7.8
ForceWare 15.08
Memory size 4GB (4 DIMMs) 4GB (4 DIMMs)
Memory type 2 x Corsair TWIN2X20488500C5D
DDR2 SDRAM
at 800MHz
2 x Corsair TWIN2X20488500C5D
DDR2 SDRAM
at 800MHz
CAS latency (CL) 4 4
RAS to CAS delay (tRCD) 4 4
RAS precharge (tRP) 4 4
Cycle time (tRAS) 18 18
Command rate 2T 2T
Audio Integrated ICH9R/ALC889A
with RealTek 6.0.1.5497 drivers
Integrated nForce 680i SLI/ALC850
with RealTek 6.0.1.5497 drivers
Graphics Diamond Radeon HD 3850 512MB PCIe
with Catalyst 8.2 drivers
Dual GeForce 8800 GT 512MB PCIe
with ForceWare 169.28 drivers
Dual Radeon HD 3850 512MB PCIe
with Catalyst 8.2 drivers
Dual Palit GeForce 9600 GT 512MB PCIe
with ForceWare 174.12 drivers
Radeon HD 3870 512MB PCIe
with Catalyst 8.2 drivers
Dual Radeon HD 3870 512MB PCIe
with Catalyst 8.2 drivers
Radeon HD 3870 X2 1GB PCIe
with Catalyst 8.2 drivers
Dual Radeon HD 3870 X2 1GB PCIe
with Catalyst 8.3 drivers
Radeon HD 3870 X2 1GB PCIe +
Radeon HD 3870 512MB PCIe
with Catalyst 8.3 drivers
Palit GeForce 9600 GT 512MB PCIe
with ForceWare 174.12 drivers
GeForce 8800 GT 512MB PCIe
with ForceWare 169.28 drivers
EVGA GeForce 8800 GTS 512MB PCIe
with ForceWare 169.28 drivers
GeForce 8800 Ultra 768MB PCIe
with ForceWare 169.28 drivers
Hard drive WD Caviar SE16 320GB SATA
OS Windows Vista Ultimate x86 Edition
OS updates KB936710, KB938194, KB938979, KB940105, KB945149, DirectX November 2007 Update

Thanks to Corsair for providing us with memory for our testing. Their quality, service, and support are easily superior to no-name DIMMs.

Our test systems were powered by PC Power & Cooling Silencer 750W power supply units. The Silencer 750W was a runaway Editor's Choice winner in our epic 11-way power supply roundup, so it seemed like a fitting choice for our test rigs. Thanks to OCZ for providing these units for our use in testing.

Unless otherwise specified, image quality settings for the graphics cards were left at the control panel defaults. Vertical refresh sync (vsync) was disabled for all tests.

We used the following versions of our test applications:

The tests and methods we employ are generally publicly available and reproducible. If you have questions about our methods, hit our forums to talk with us about them.