Question about crossfirex/sli vs dual gpu

[wong93]

1)Is there really any difference bewteen these??


2)Which one would be cheaper in terms of price when compaing dual gpu vs dual gpu in crossfire?

for example an AMD HD 7990 vs dual 7970 in crossfire mode??

 

[hytecgowthaman]

Gpu set up look like this. 1x gpu=x16; 2x gpu=x16+x16=(x32); 3x gpu=x16+x8+x8=(x32); 4x gpu=x16+x8+x4+x4=(x32). so 2xgpu=4xgpu.
Possible:
7990 + 7970
690 + 680
or
7990 + 690
7970 + 680
some games work in 7990 and not work in 690,some games work in 690 and not work in 7990.
so play all games by inserting two company gpus in one system.