Sometimes 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 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.
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
When SLI was first introduced the technology was used only to connect multiple video cards. 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.
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.
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.