What is Scalable Link Interface (SLI)?
NVIDIA created SLI, a technique that enables numerous graphics processors to cooperate in a single computer system. Through this, visual capability can be achieved more quickly than with a single device. For instance, connecting two video cards via SLI could provide up to twice the speed of a single video card. The speed of a normal video card could increase by up to four times if each card has two Processors.
The machine needs to have numerous PCI Express ports in order to connect video devices using NVIDIA's SLI technology. Because the ports share a network, PCI Express is the first video card protocol to support connecting of numerous graphics devices. Graphics devices could not be linked because earlier systems, like PCI and AGP, used distinct networks. The PCI Express ports must be x8 or x16 spaces in order to provide the devices with the necessary capacity. Of course, for SLI linking to function, the devices themselves must also enable it.