ATI'S way of doing SLI called AMR (ATI Multi Rendering) will work differently from Nvidia's now world famous SLI. ATI will make its SLI work without a small printed circuit board (PCB) to interconnect the cards.
SLI uses two PCIe graphic ports and in the case of Nforce 4, works at PCIe 8X for each card and renders your picture with both cards. For this operation Nvidia SLI needs a special interconnection between two graphic cards. It’s a small cable or PCB that transfers up to four GB per second from one card to another. For this operation, coordination is crucial as one card needs to know what the other card is doing.