Originally Posted by Scorpion49
No, they like to combine the number to make it sound "bigger, stronger, and faster than before". A 3GB GTX 590 has 1.5GB per GPU, a 4GB 6990 has 2GB per GPU. The Vram is mirrored in an SLI/CF setup because both are doing the same work, but calling it a 2GB or whatever makes it sound slow to the average joe who doesn't even know anything other than bigger numbers are better.
All of the dual GPU cards are essentially CF/SLI without the motherboard in between.
Like Scorpion49 said, the ram is all on one board, but 1/2 is allocated to one GPU, and 1/2 is allocated to the other. I have the 5970 (5870 dual GPU at 5850 core speeds) with 2Gb vRAM. When I run eyefinity, more ram is better for fram buffering. But the ram is not combined, I only have 1Gb usable ram for the 5970 to utilize.