ATI Multi Rendering
ATI Multi-Rendering (AMR) is a video technology which enables a single computer to use more than one video processor. Created in 2002, AMR uses a technology ATI calls "Super Tiling" to connect multiple (two or more) video cards together. Up until the point ATi starts marketing it for the mass market, it has been primarily used by Evans and Sutherland, for commercial flight simulators, because of its ability to use more than two VPUs.
Super Tiling
Super Tiling is a technology that splits the screen up into equal divisions whose size is based on the number of VPUs. These divisions are called tiles. The partial images are then put together and displayed on the screen. All though not much is known about the interconnect method. it may be a device that bridges the cards together in a method similar to nVidia's SLI bridge card, or it may pass data over unused PCIe ports (as each card will be on a 16X slot, but will only be working at 8X interconnect rates)
Release
The official name of AMR's commercial variant is known as Crossfire. The chipset was launched with ATI's R520 core for Intel and AMD platforms in the summer of 2005.
Performance gains
Because of its ability to connect more than two video cards together (as many as 34 cards have been coupled by Evans and Sutherland, though you will not be able to have this many VPUs in your desktop), performance will be much higher than that of the current SLI cards built around the nVidia video processors which can only couple two cards together.