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Originally Posted by cadaveca SLi allows either frame swapping, or half-screen. It really all depends on which game it is...and they need to be supported by the driver. I am sure that the driver support will expand greatly with updates, but they only about 25 or so games currently supported. |
SLI really shouldn't need designed-in game support for frame swapping to work. Look at it this way - where the game (or operating system) is concerned, there is only 1 display and 1 frame buffer to write to. This is actually the case, however many cards there are in parallel here.
In a 3D game, the graphics card is working on effectively 3 things: 1) a set of n translation matrices (forward and inverse) for each visible or nearly visible object in range to determine position, velocity and acceleration. 2) For each visible object, surface/texture mapping. 3) For each surface, the effect of lighting. If you allow that to set the first screen up takes maybe a millisecond longer in SLI than in a single chip system (to calculate the coordinates of all objects after a discrete time interval), then one GPU can work on all odd numbered frames entirely independently of the second GPU working on all even numbered frames. The image itself only actually comes together when all the components (coordinates, surface, T&L) are blended together in the frame buffer. As such, the game need not actually be aware that the hardware is splitting the work up between n processors.
What will be interesting is what happens for subsequent driver revisions - obviously the card with the monitor attached has to work harder, since it has to process the final picture. It will be interesting to see how the components of making a frame are broken up between the two cards to keep both at maximum capacity.
If games really do require support for SLI to be designed in, then this shows poor forethought on nVidia's part in how they represent the SLI to Windows.