Introduction

I've been excited by SLI ever since it was introduced as Scan Line Interleave by 3Dfx. Two Voodoo2 cards could operate together, with the noticeable benefit of upping your maximum 3D resolution from 800x600 to 1024x768. Amazing stuff...back in 1998.

Fast forward almost twenty years. 3Dfx went out of business long ago (it was acquired in 2000 out of bankruptcy by Nvidia), and SLI was re-introduced and re-branded by Nvidia in 2004 (it now stands for Scalable Link Interface). But the overall perception of SLI as a status symbol in hardcore gaming machines, offering massive rendering power, but also affected by numerous technical issues, has changed little.

Today we're looking at the green team specifically, and we plan to follow up with a second part on AMD's CrossFire. In that next piece, you'll see us compare both manufactures' dual-GPU offerings.

Note

Some ideas in this article come directly from users we surveyed on Reddit. Thank you to all those who contributed!

In this article, we'll explore some of the technology's basics as it operates today, take an in-depth look at scaling with two cards compared to one, discuss driver and game-related issues, explore overclocking potential and finally provide some recommendations on how to decide whether SLI is right for you.

While SLI technically supports up to four GPUs in certain configurations, it is generally accepted that three- and four-way SLI don't scale as well as a two-way array. While you are likely to see PCs with three or four GPUs at the top of synthetic benchmark charts, they're a lot less common in the real world, and not just because of their cost.

Furthermore, Nvidia representatives confirm that three-way SLI is not supported in 8x/4x/4x PCIe lane configurations, which are native to Intel's LGA 1150 platform. You'll either need an LGA 1150-based board equipped with an (expensive) PLX bridge chip or an even more expensive LGA 2011-v3 platform if you want to go beyond two-way SLI. Fortunately, most Haswell/Ivy Bridge/Sandy Bridge platforms enable two-way SLI without issue.

Finally, another downside of going beyond two-way SLI is that, because of the way SLI works, input lag increases as the number of cards working together goes up.



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