GeForce 6/Quadro SLI
In addition to native PCI-Express compatibility, some members of the GeForce 6 support a trick borrowed from the old 3dFX Voodoo2: SLI. SLI (3dFX referred to SLI as scan line interfacing, while nVIDIA uses SLI to refer to scalable link interfacing) uses two identical video cards connected together to run a single monitor. Each video card is responsible for refreshing part of the screen, boosting performance. While the 3dFX version of SLI used each video card to draw alternate lines (1,3,5,7, and so on) and lines 2,4,6,8, and so on) on a single monitor, GeForce 6's implementation of SLI uses load balancing, assuring that each GPU will do about the same amount of work in rendering a scene. For example, if 25% of the screen is constantly changing in a given game, but the remainder of the screen is relatively static, load balancing will divide up the workload accordingly.
While the old 3dFX Voodoo 2 used a pair of PCI slots, meaning that almost any system could use SLI, the GeForce 6 version requires motherboards with a pair of PCI-Express slots. These motherboards will be identified as Multi-GPU Ready, and will be available in late 2004 and early 2005. The latest Quadro technical workstation GPUs also support SLI.