GeCube introduced a dual GPU card based on 2 Radeon X1600 XT named Gemini Edition. The interest of this card is rather limited because the X1600 XT CrossFire performances (in "software mode", without compositing engine) aren't extraordinary and because it is announced at a probable price of 400€. This figure has to be compared, for example, to the 250€ of a X1800 GTO which provides much higher performances. GeCube doesn't deny this fact and says that this solution is interesting mainly because of the four monitors supported by the 2 dual DVI outputs.
The thing is that the functioning of this card is isn't very explicit. Interrogated on this subject, GeCube confirmed us that a chip was included for the two CPU to communicate. We couldn't get more information and GeCube refused to let us take a picture of the PCB without the cooling system to avoid breaking an NDA with ATI. This is the reason why we thought that there was something more interesting behind this card. All the more that Gemini is a technology that is found in some of ATI's roadmaps...
Our interpretation, based on several little details that match, is that Gemini could be a chip in charge of managing exchanges between the two GPUs and the PCI Express bus. It would be some sort of switch used to connect the 2 GPUs to a single port but also to bring a direct access, a little bit more efficient, between the two GPUs without using the chipset (NVIDIA uses a chips that is apparently similar for dual 7900 used in the Quad SLI).
But how could a card such as Asus' bi-7800 GT, that we have tested, work without a chip of this type? In fact with this chip, each GPU connects to the chipset in PCIE 8x, but it only works with the nForce 4 SLI. It seems that this system only functions if the chipset is capable of using a single PCI Express port like 2 distinct ports and ATI's recent Xpress 3200 wouldn't be capable of doing that. A special chip would have to be used with dual GPU cards. This chip could also be used to improve gains brought by the CrossFire to cards that communicate via the PCI Express bus by allowing an optimised inter GPU access.
Gemini could be found on the RV560 and RV570 GPUs that will be announced this summer and, if our speculations are verified, it could be a solution that would allow the development of more interesting dual GPU cards (higher performances) and not only intended to round up ATI's chipset limitation to have a card that support four monitors.