The ASUS Extreme N7800GT Dual video card is a single Printed Circuit Board (PCB) that has incorporated on it two GeForce 7800 GT GPUs. Both GPUs are wired on the PCB with SLI automatically connected between them. That bridge chip you have to install between two graphics cards in SLI is basically built into the PCB so that both operate in SLI with no hardware to change. This of course does mean that the video card itself is larger; needing the room to fit two GPUs with RAM for each on one card, and it also runs hotter and requires more power. You basically have two video cards all rolled up into one card, so the demands are much higher.



Link: HardOCP