nVidia SLI Technology
A lot of people have no idea what SLI is, or what it does. SLI (Scalable Link Interface) allows your computer to use two video cards at once and it improves your video performance. To use SLI you need to have a PCI Express motherboard that supports SLI, currently only the NVIDIA nForce 4 chipset supports it. The board must have two 16x PCI-E slots, and you must have 2 identical video cards that support SLI, like the GeForce 6 series GPUs.