The xDNA technology is a technology designed by Diamond Multimedia, allowing motherboards which are not certified for ATI CrossFire (for instance, nForce 500/600 series motherboards designed by NVIDIA) to install multiple ATI Radeon video cards (up to four) as a CrossFire setup and operate in rendering modes which are exclusively made for CrossFire setups. Diamond Multimedia will provide optimized Catalyst Drivers and middleware for the platform in a single package.
References
XDNA (multi-graphics) Wikipedia(Text) CC BY-SA