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Introducing the Multi-GPU Index


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Introduction


Let's face it the ability to link more than one video card together has become a huge driving force in the enthusiast PC market and is often a topic of discussion in motherboard reviews ever since the announcement of nVidia SLI back in 2004.  Since then, PC gamers have desired more and more power when gaming.   In some cases, instead of pouring cash into a single high-end video card, they opt for a competitively priced model with the intent of adding a second video card later.  

Using multiple video processors isn't a new idea; 3dfx pioneered the process with the Voodoo2.  3dfx SLI, or rather "Scan-Line Interleave", allowed 2 or more Voodoo2 cards to be linked together which almost doubled overall video performance.   AGP saw the first dual processor video cards both from 3dfx and ATI, however bandwidth and processing power were limited by the single AGP video connection.  It wasn't until the advent of PCI Express where we saw the re-emergence multiple graphics cards and a new leap in video performance.

PCI Express is a high speed serial replacement for older parallel technologies like PCI and PCI-X.  The new architecture also replaced AGP as the primary path for video processing due to the higher bandwidth and modular design.  The simplest way to think of PCI Express is to describe the notion of "Lanes".  Each lane is a single full duplex signal path than can carry between 250 and 500 MB/s of data.  These lanes can then be grouped together in factors of 2 (1x, 2x, 4x, 8x, 16x) up to a maximum of 32x.  

This article will be centered on the "factors of 2" limitation and how it translates into basic motherboard design and layout.  The results we gather will be used to create the first ever Ninjalane Multi-GPU Index.
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