I apologise if this has been covered elsewhere, but I am extremely confused as to how ATI's X2 and nVidia's GX2 series relate to Crossfire and SLI respectively - with regard to drivers that is.
I understand that to get two discrete cards to work together, you need SLI/Crossfire support in the driver - after all, the cards are completely separate, with separate bus IDs, and have to be managed in order to get them to work together.
However, for single-card, dual GPU setups (the GX2s and X2s of this world), why do you need special support in the driver? Should this not be handled in hardware, and be completely transparent to the driver, in the same way that an SATA hard disk can be "hidden" behind a Firewire bridge chip, and only expose the firewire personality to the host computer?
With a X2/GX2 are two bus IDs exposed onto the PCIe bus, or just one? Am I just confused and talking rubbish?