What is NVIDIA SLI Technology?
NVIDIA® SLI™ technology is a revolutionary platform innovation that allows
you to intelligently scale graphics performance by combining multiple
NVIDIA graphics solutions in an SLI-Certified motherboard.
How Does SLI Technology Work?
Using proprietary software algorithms and dedicated scalability logic in
each NVIDIA graphics processing unit (GPU) and MCP, NVIDIA SLI technology
delivers up to twice the performance of a single graphics solution. more info
90% of gaming performance
is achieved by the graphics card itself.
Crossfire is the same as SLI except it utilises ATI cards instead of nVidia. more info
The cards can be taken out of SLI or crossfire configuration and then up to 4 monitors can be used instead.
SLI & Crossfire Graphics card comparison chart