Bus Routing In ATI Crossfire

Onto ATI's Crossfire implementation. By looking at the ATI reference board, we can see that the second PCIe slot needs a “signal forwarding” card to be slotted in when the motherboard is running with only a single ATI graphics card.

Bus Routing In Crossfire

The “signaling forward card” is needed to forward the 8-lane PCIe bus of the second PCIe slot back to the first PCIe slot so that the single PCIe card can benefit from all 16-lanes - thereby running at 16x PCIe.

However, DFI has taken a different approach in the RD482, as they have decided to implement a "switching solution". In this design, the “signal forwarding card” is not needed as the 8-lane PCIe bus for the second PCIe slot is now directed to the switch. Then, the switch decided which PCIe slot should receive the signals from these 8 lanes. This can be either the first PCIe slot (single card) or the second PCIe slot (dual cards).

Final Updates

After receiving numerous feedbacks, DFI has made some changes to their nForce4-based motherboards. The upcoming (new revision) of the DFI SLI motherboard will feature 3 PCI slots as well as a Promise SATA controller. The layout, particularly the upper part, has also been redesigned.

Questions & Comments

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