Crossfire on P965

P965 with dual graphics

The Crossfire incompliance is a pity, as there are plenty of reasons why one would prefer a P965 mainboard above a 975X. First of all the lower price makes it worth considering a P965 board, but most of all the far better overclock potential, because of the more advanced chipset, makes this board quite attractive. Overclockers already succeeded in lifting the P965 FSB up to frequencies above 500 MHz. In addition the P965 also contains the modern ICH8(R) south bridge. Furthermore our tests have been showing us that on performance level the 975X and P965 are as good as equal. Actually, Crossfire occured to be the only benefit of the 975X...

Until ATI introduced the 6.9 Catalyst drivers, allowing a Crossfire setup on P965 mainboards with two VGA slots. As we stated before the north bridge lanes on a P965 cannot be divided into 2x 8 lanes, so mainboard manufacturers had to figure out a trick: the first card is controlled by all sixteen PCI-Express lanes od the north bridge chip, while the second one is connected to the ICH8 south bridge with four lanes. Instead of a 8x8 Crossfire configuration this creates a 16x4 configuration.

ASUS P5B Deluxe mainboards are equipped with the C.G.I. technology to speed up Crossfire setups

CGI

Ofcourse Crossfire on a P965 is not as fast as a setup on a 975X board. Beside the four lanes bottleneck of the second graphic card, there is also a delay because of the extra chip it takes to communicate with this card. Data needs to be transported from the processors to the frontside bus, then to the south bridge and after that via the DMI connection to the south bridge.

To speed up Crossfire setups on P965 mainboards ASUS has introduced the C.G.I. technology within a new BIOS on her recent P5B-series. C.G.I. stands for Cross Graphics Impeller, but that's about everything ASUS has been revealing on the technology. However it seems pretty obvious C.G.I. consists of BIOS optimisations on the DMI-interface between the north and south bridge chip. ASUS claims a huge boost on performance, which should allow P965 Crossfire scores to approach the 975X scores.

P965 mainboards with two VGA slots

The following P965 mainboards we have been testing, contain two VGA slots and therefore are compliant to Crossfire with ATI Catalyst 6.9:

ASUS P5B Deluxe Wifi-AP Edition

ECS P965T-A

Gigabyte 965P-DQ6

MSI P965 Platinum