What is CrossFire & CrossfireX? What is SLI? How SLI Performs?

Previously called CrossFire, AMD CrossFireX (as it is called today), refers to a brand name for the multi-GPU system by Advanced Micro Devices which was in fact originally developed by ATI.

What is CrossfireX ?

Crossfire-X technology allows you to connect two or more of the same family GPUs together for combined performance. The great thing about CrossfireX is that you do not slow down the faster GPU's clock rate when running it in conjunction with other graphics processors. So for example, if you run a Radeon 7950 and a 7870 together in CrossfireX configuration, that is fine. This differs from Crossfire and SLI which required you to pair the same GPUs together.

What is SLI?

Since it was the first of the two technologies to be released. SLI was originally introduced by 3dfx in 1998 with their Voodoo 2 card. At that time SLI meant Scan Line Interleaving and worked by making each GPU to process one group of lines (one GPU processing odd lines and the other processing even lines). NVIDIA bought 3dfx on April 19^th 2001 and introduced a similar but updated concept for their video cards in June 2004, renaming SLI to Scalable Link Interface.

SLI Works :

• SFR (Split Frame Rendering), where each frame is divided in two and each half is sent to a different GPU to be processed. This is the mode used by SLI configurations using two video cards.
• AFR (Alternate Frame Rendering), where each GPU processes an entire frame, but while one GPU is processing the current frame, the other GPU is already rendering the next frame, so when the first frame is delivered, the second frame is already rendered (ideally) or almost rendering. This is the mode used by three-way SLI.
• AFR of SFR, which is used on Quad SLI system. Here two GPUs process the first frame under SFR mode while the other two GPUs are processing the next frame also under SFR mode.