Tom's Hardware Guide has compared ATI's CrossFire with NVIDIA's SLI.
NVIDIA was first to offer a platform for deployment of a graphics card couple. The technology is called Scalable Link Interface (SLI) and is available in a number of NVIDIA nForce4 chipsets for either AMD or Intel processors. ATI announced its Crossfire Multi Video Processing (MVP) counterattack earlier this year, but was not able to actually ship the product - until now.