What is SLI and how does it make things better?

Posted: January 15, 2012 in INFR 2350
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Disclaimer: I am by no means an expert, professional, or entirely educated on this topic. This will be a general explanation/overview on what I know and what I can share. 

SLI stands for Scalable Link Interface which was developed by Nvidia as a multi-GPU solution. This allows a user to link two or more video cards (GPUs) together to create a single output from the GPUs working collectively. All of this creates parallel processing, which increases the power/performance for graphics in a computer. Similarly AMD also has their own multi-GPU solution for their GPUs called CrossfireX. I will only be talking about SLI from Nvidia, but some of the things can be applied to AMD’s CrossfireX.

The number of GPUs you can put together using SLI is dependent on your motherboard (and your budget haha), whether or not it is SLI certified or has enough slots to host several GPUs on it. Also a user must have a power supply unit that is capable or providing enough power to the additional cards.

How do I use SLI?

To use SLI, in addition to having a capable motherboard, your video cards must have the identical GPU. They can be different brands, clock speeds, BIOS revisions and memory size, but the GPU series itself must be the same to work with each other (ex. you can SLI an EVGA GTX560 Ti and a Gigabyte GTX560 Ti together, but you cannot SLI an EVGA GTX480 and an EVGA GTX 290 together).

So what does SLI do for me graphics wise? 

Besides just better performance overall, if two GPUs are SLI’d together, while running PhysX based applications (games) one GPU can be dedicated entirely towards the calculation of the physics in the game, while the other GPU handles all the rendering within the game and the graphics related processing. Working together, they produce one output of all the physics calculation and graphics processing to create realistic outputs. The increased performance also increases the framerate of applications.

The graph shows the dramatic increase in framerate with the help of an addition GPU to increase the graphics performance

What else can it do for me?

If you’re looking for a performance computer to chew away at graphic processes, such as a gaming computer, but don’t want to buy the highest end card, SLI is often a solution.

By combining 2 GPUs that slightly under perform a higher-end GPU, often the setup can exceed or match the high end GPU’s output. An example is a benchmark test at Tom’s hardware where 2 GTX460 that are in SLI configuration are put up against a GTX480. During the benchmark test, the SLI configuration of the two GTX460s wins every time with a significant margin.

http://www.tomshardware.com/reviews/geforce-gtx-460-sli-geforce-gtx-480,2694-9.html

Even though as of this blog post the GTX400 series GPUs have been replaced by the GTX500 series, using the 500 series pricing here is an example of the cost benefit of SLI:

GTX580 card is around $500, where a GTX560 card is under $200. You can get better performance (assuming the 500 series have similar benchmarks to the 400 series, probably not, but I’m just using this as a price reference for the 400 series) for more than $100 less than a high end video card if you are on a budget!

Personally I find it a worthy investment to SLI GPUs. Another way to approach this to invest in a high end GPU now, and later when it starts to get “out of date” you can buy the same GPU for a cheaper price and SLI it. This will give you a performance boost you need to stay ahead of the game.

An SLI comparison to a Non-SLI application. Generally the SLI video is smoother and has more detail I suggest watching it at the highest resolution to see things better. 

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