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sli performanceSometimes a niche term is taken for granted. We have some such terms in the world of computing hardware, and one of them is SLI. It’s been around for so long that geeks take it for granted. Everyone knows what SLI is and how it works, right? Sure – except, perhaps, for people who haven’t been following hardware for the last ten years.

Now is your chance to catch up.

SLI – Breaking Down The Acronym

sli performance

SLI technically stands for Scalable Link Interface. It is the term used by graphics card company Nvidia to describe the way it connects multiple GPUs. The technology is a form of parallel processing that makes it possible for up to four Nvidia GPUs work together to render a game at extremely high frame-rates.

However, as so often happens, the term SLI is often used generically to describe all similar technologies. Competitor AMD uses the name CrossFire to describe its own version of this concept, but enthusiasts will sometimes call it SLI by mistake or because they don’t feel like typing out the entire word “CrossFire.”

There’s also a company called Hydra which makes a chip that allows multiple GPUs, even those from different brands, to work as one. This too is sometimes generically referred to as a form of SLI.

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Whatever the situation or the brand, if someone brings up SLI, they’re talking about using multiple GPUs to render a game.

It’s Not Just For Multiple Video Cards

sli performance gain

When SLI was first introduced the technology was used only to connect multiple video cards How To Choose The Right PC Video Card [Technology Explained] How To Choose The Right PC Video Card [Technology Explained] Read More . In 2005, however, Gigabyte introduced a video card that used SLI technology to connect two different Nvidia GPUs located on the same video card.

This arrangement has become more common over time. Both Nvidia and AMD have released reference design cards featuring two GPUs in the same video card connected via SLI or CrossFire. This has confused things a bit because two video cards with two GPUs each would technically be a quad-SLI arrangement even though only two video cards are involved. With that said, these cards are expensive and thus rare, so you can generally assume that if someone is talking about SLI they are talking about the use of two or more video cards.

SLI usually describes a desktop solution but it is available in gaming laptops. AMD sometimes pairs its APUs with a discrete Radeon GPU, which means you’ll sometimes run across CrossFire laptops that only cost $600 to $800 bucks.

Nvidia has also paired a discrete GPU with an integrated GPU in the past. This was branded with the term Hybrid SLI. Nvidia was forced out of the chipset business soon after, however, which meant the company no longer offered integrated graphics. Hybrid SLI is effectively dead as a result.

Compatibility

sli performance gain

When SLI originally debuted it was intended to connect two video cards with the same GPU. The cards could be from different manufacturers but they had to be from the same Nvidia series. This is still generally the case. There are exceptions, but they are few and generally not worth the trouble.

AMD’s CrossFire debuted with the same restriction has since enabled the ability to use different video cards from the same sub-series. This means you can use a Radeon 6750 with a Radeon 6770, for example. However, the all cards will run at the clock speed of the slowest card.

As mentioned earlier, there is a third party option from a company called Lucid. This company is independent of either Nvidia and AMD and produces a chip that lets multiple GPUs from different generations and companies work together. The chip is integrated on some high-end motherboards.

Performance

sli performance

Many people unfamiliar with SLI assume that two cards will be twice as quick as one. Various companies selling desktops, laptops and video cards have done nothing to deny this.

The assumption is incorrect, however. There is an overhead associated with getting two or more GPUs to work together. Driver and game support for the feature are also factors. In a best-case scenario an SLI configuration will be 80% quicker than a single card. In a worst-case scenario it may actually be slower.

All versions of SLI have come a long way over the years, but there can still be problems. One common issue is micro-stutter. This is a perception of stutter that players sometimes experience with SLI configurations but doesn’t show up in a game’s average framerate. A number of articles by hardware review sites have shown that micro-stutter is a real thing, not a perception.

Conclusion – Should You Be Interested?

To be blunt, I think SLI kind of sucks in all its implementations. It has always struck me as something people buy because it’s cool (I’ve got four video cards bro!) rather than because it works well. If you want smooth, trouble-free gaming, just buy the quickest single GPU video card you can afford.

Hopefully you understand SLI better now that you’ve read this article. If you have any questions about it – or you disagree with my assessment of SLI performance – let us know in the comments.

Image Credit: PCI David, J. KleynPC Perspective

  1. Scott Ferrell
    August 26, 2015 at 2:10 pm

    curious how to find out if a laptop is SLI capable. how about if it is sold with a SLI capable GPU (e.g. geforce gtx 970m)? if you have 2 GPUs, are you able to push 3d?
    thanks in advance!

    • Scott Ferrell
      August 27, 2015 at 1:42 am

      it appears few laptops are SLI certified. the 1 SLI certified laptop i know is the aorus x5 which uses 2 965m gpus on the same video card, as indicated in column above. it's impressive but a little pricey, ~ $2200.

  2. Scarlett foxx
    May 15, 2015 at 2:59 pm

    does sli can increase gaming performance

    • Ben Hiers
      May 28, 2015 at 12:57 pm

      From what is explained here, and from slight experience, im no expert. It seems there is only a slight increase in performance mainly dealing with Fps and quicker loading, It seems like it will only make your computer faster, not exactly handle a game better but, just makes the computer faster, I have 1 970, and my best friend has the SLI with 2 760s, he plays his games around high settings and im on ultra, but i noticed his game will start up wayyyy quicker than mine and has shorter loading screens. and it's not because of the processors we have the same processor, im not sure it's worth it especially with how vague it is with what it does.

      • Alexander Brorson Olsen
        August 27, 2015 at 5:10 pm

        2-way SLI improves fps/performance by around 80%.

    • John W. Shek
      February 28, 2016 at 5:35 am

      yes it does, in speed and frame rate, i had one gigabyte 6gb 980 ti g1 xtreme waterforce all in one graphics card and it scored around 3000 in unigene heaven benchmark and a max fps of 233, real fps at 122, i swapped that out for two 780 3gb asus watercooled Poseidons, yes for bad ass looks and also performance which gave me a score on the same benchmark of 3652 and a max fps of 261 and a real fps of 145. So yes it does look better and also performs better.

  3. James
    April 20, 2015 at 3:36 pm

    But wouldn't an SLI option be cheaper seeing as you already have the card itself and less expensive by getting another 670 than buying a brand new 980?

    • David Gonzalez
      September 22, 2015 at 2:52 pm

      The motherboards that support SLI are typically slightly more expensive. However, you are correct. Also the added cost on video cards that support SLI is also quite large $200 minimum most cases for a 2-way SLI card.

  4. Kevin
    September 28, 2012 at 1:52 pm

    Can I use SLI on LGA 775 board?

  5. Shawn Ashree Baba
    July 18, 2012 at 1:35 am

    Hopefully the technology behind SLI booms. Can't wait to see where things will go from here on out.

  6. Doc
    July 8, 2012 at 6:50 pm

    "When SLI originally debuted it was intended to connect two video cards ... from the same Nvidia series."

    Actually, the first version of "SLI" stood for "Scan Line Interleave," and it connected two video cards from 3DFX, with each card rendering either odd or even lines (thus sharing the workload). After 3DFX's bankruptcy, nVidia bought out their technology portfolio (which was eventually incorporated into the GeForce 5 series cards), and the meaning of SLI was changed to what nVidia terms it today.

    • Matt Smith
      July 9, 2012 at 1:40 am

      I think you're half right. 3Dfx did have a technology called SLI and Nvidia did buy it with the company's technology portfolio. However, I can't find anything that says modern SLI is based off the technology 3Dfx used.

      NVIDIA's version uses split-frame or alternate-frame rendering while 3Dfx used interwoven frame rendering where each card rendered alternating lines of the same frame.

      • Doc
        July 9, 2012 at 6:46 pm

        Nowhere did I say that nVidia's SLI used any 3DFX technology; its GeForce 5 line incorporated some of the useful technology, though. IIRC, nVidia didn't debut its SLI technology until several generations later.

        nVidia's SLI uses a completely different model; IIRC, it uses the framebuffer(s) of whatever card(s) are doing video output (one or more monitors attached) among all cards (including Hybrid SLI, which can also use a motherboard-based GPU and/or several compatible cards), dividing the workload based on need and capabilities...something totally impossible with 3DFX.

        (I still have a Diamond Monster 3D and a couple of Banshee AGP cards lying around...nostalgia!)

  7. Wiry Andi
    July 7, 2012 at 4:13 am

    So uh... with SLI we can connect 2 or more video card right?
    does all of the video card must have SLI support in order to be able to work together?
    and why in some case, SLI make it slower than single video card performance?

    • Matt Smith
      July 9, 2012 at 1:41 am

      Yes, you need two or more SLI compatible cards.

      SLI can sometimes be slower than a single video card because of driver problems. It is not a common situation but has occasionally occurred with newly released games. The problem, if it does occur, is usually resolved by the next driver release.

      • Wiry Andi
        July 28, 2012 at 2:06 pm

        But, when more than one video card work together and it is slower, can it be fixed?

  8. Dan T
    July 6, 2012 at 8:10 pm

    I agree with your conclusion that SLI sucks. I added a second card to my setup with Crossfire and it made no noticeable difference other than fan noise and more heat. A single card solution works better for me.

  9. Laga Mahesa
    July 5, 2012 at 5:30 pm

    Very informative, cheers - I agree with your conclusion. Not worth it overall, especially if you add the SLI debugging to the usual driver debugging hardcore gamers seem to enjoy.

    However you've focused on gaming - is there no other application? What about pro apps that support hardware acceleration: graphics, video processing, etc? Serious question, inquiring minds wish to know!

    • musicphann
      July 5, 2012 at 7:14 pm

      Sounds like it would be useful for 3d(Blender, Maya, etc.). Many modern render engines support GPU rendering.

    • Matt Smith
      July 6, 2012 at 10:19 pm

      Some professional apps do benefit from SLI and I also know that GPU-compute is sometimes used for supercomputing. SLI can be very useful in these situations, but it was a bit outside the scope of this piece. Besides, I figure if you are looking to build a supercomputer you already have a decent amount of hardware knowledge.

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