2-way and 3-way AMD CrossFire and NVIDIA SLI scaling on Intel Sandy Bridge

What do you do if you have a pile of AMD Radeon HD 6970 and HD 6950, and NVIDIA GeForce GTX 580 and GTX 570 graphics cards? In this review / shootout, VR-Zone.com tests multi-GPU CrossFire and SLI scaling performance of the latest graphics cards on Intel’s new Core i7-2600K CPU and the ASUS Maximus IV Extreme motherboard!

Introduction

While others are busy testing the new Intel Core i7-2600K Processor and Core i5-2500K Processor, we found comfort in burying ourselves under a pile of graphics cards. The Sandy Bridge platform is mighty fast; the new processors can easily attain 4.5GHz clocks on air cooling and the integrated memory controller can run memory at 2133MHz without breaking a sweat. Don’t you think this is an excellent candidate to chase your multi-GPU setup dreams? With such high operating speeds, the most common (and dreaded) bottleneck – the CPU – is allievated.

Before we begin, let us take a look at the discrete graphics portion of the new Sandy Bridge platform. LGA 1155 has native support for 16 PCI Express 2.0 lanes across a maximum of just two devices. A single graphics card would operate in x16 mode, but on a two-card AMD CrossFire or NVIDIA SLI configuration, each graphics card operates at only x8. In comparison, the LGA 1366 platform provides a total of 36 PCI Express 2.0 lanes, easily accomodating four graphics cards in a x8/x8/x8/x8 configuration.

In order to run three graphics card in CrossFire or SLI on the new Intel Sandy Bridge platform, a PCI Express bridge chip such as the NVIDIA NF200 must be used. We have chosen the ASUS Maximus IV Extreme motherboard, which has the NVIDIA NF200 bridge chip built-in. As mentioned in our preview, the first and third red expansion slots are routed directly to the CPU, while the second and fourth slots are routed to the NF200 chipset.

When running a single graphics card, we used the first expansion slot for the full 16 lanes running directly off the processor. It is recommended that the NF200 be used only when running three-card configurations as bridge chips add latency. For our two-card tests, we used the first and third slots for a x8/x8 configuration, again running directly off the processor.

For our three-card tests, we used slots 1, 2 and 4. Slot 2 and slot 4 are full PCI Express 2.0 x16 lanes connected to the NF200 chipset. The first graphics card operates at x8, while the NVIDIA NF200 presents itself to the processor as the ‘second device’, also running at x8. Data between the second and third cards on the NF200 and the processor is routed internally by the chipset itself.

Test setup

Our Intel Sandy Bridge platform test bed consists of the following parts:

• Intel Core i7-2600K Processor, at 4.7GHz (100 x 47)
• Thermalright Silver Arrow
• ASUS Maximus IV Extreme (Intel P67 Express)
• Kingston HyperX T1 DDR3 2133MHz 4GB Kit (KHX2133C9D3T1K2/4GX)
• Cooler Master Silent Pro M1000 PSU
• Western Digital Caviar Blue 500GB SATA HDD
• Dell UltraSharp 3007WFP LCD
• Microsoft Windows 7 Ultimate 64-bit
• AMD Radeon HD 6970 2GB
• ASUS EAH6970/2DI2S/2GD5 (Radeon HD 6970)
• Sapphire Radeon HD 6970 2GB
• 3 x Sapphire Radeon HD 6950 2GB
• 3 x Palit GeForce GTX 580 1536MB
• 3 x Palit GeForce GTX 570 1280MB
• AMD Catalyst 10.12 WHQL
• NVIDIA Release 263.09 WHQL
• NVIDIA Release 265.90