So usually the cards do not use the PCI Express bus to transfer data between them – and that is why using the PCI Express slot under x8 mode isn’t so problematic. The communication between the video cards is done through a private connector, called SLI bridge. Keep in mind that depending on the chipset the x16 PCI Express slots can run at x8 speed when SLI mode is enabled (more on this later). SLI is available only with PCI Express cards and you need to have a motherboard with two (or three, in the case of 3-way SLI) x16 PCI Express slots and the motherboard must be based on an NVIDIA chipset (the only exception is the Intel Dual Socket Extreme platform – codename SkullTrail – which is based on the Intel D5400XS motherboard which supports both SLI and CrossFireX technologies).
#CROSSFIREX VS CROSSFIRE WINDOWS#
So far this mode does not work under Windows Vista.įigure 1: Split Frame Rendering (SFR) mode.įigure 2: Alternate Frame Rendering (AFR) mode. While with a single video card you can typically only obtain up to 4x or 8x anti-aliasing modes, with SLI this number is elevated to 8x, 16x or 32x, depending on the SLI mode. In fact under this mode the game usually runs slower but with a better image quality. This mode isn’t intended to improve gaming performance but increasing image quality. Here two GPUs process the first frame under SFR mode while the other two GPUs are processing the next frame also under SFR mode. AFR of SFR, which is used on Quad SLI system.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 SLI configurations using two video cards.
SFR (Split Frame Rendering), where each frame is divided in two and each half is sent to a different GPU to be processed.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. 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). SLI was originally introduced by 3dfx in 1998 with their Voodoo 2 card. Let’s start first talking about SLI, since it was the first of the two technologies to be released.
With the recent release of CrossFireX by AMD/ATI and 3-way SLI by NVIDIA we think it is a good time to make a technical comparison between all incarnations of these two technologies, which have the same goal: to allow video cards to be connected in parallel in order to increase gaming performance.
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