Getting two or more graphics cards to do one single job sounds like an amazing idea in theory but in reality, it might not yield such extraordinary results.
There were a host of issues that plagued both AMD’s Crossfire and Nvidia’s SLI, both valid approaches to the multi-GPU idea, but neither can really brag about solving their issues properly.
When these technologies made their debuts in the mid-2000s, many were excited about the implicit promises they made. However, the lukewarm start both of these companies offered for their respective multi-GPU solution, would, unfortunately, continue throughout their entire lifespans.
Crossfire was officially put to sleep in 2017 and while SLI still technically has a pulse, it has now been replaced by NVLink, depending on who you ask. Even though Nvidia’s SLI upgrade does technically offer a massive enhancement, and one could even argue that previous generations soured the tech world on the idea.
What might’ve been the kill shot for the general idea of two or more graphics cards working as one, is the advancement of technology and the fact that modern high-end GPUs simply have very little problems handling even the most demanding video games at the highest settings.
As such, both SLI and Crossfire (and by the looks of things, NVLink) will go down in history as something that only enthusiasts found valuable enough to use.
Still, the very idea is fascinating and here we’ll take a look at how both of these technologies work, as well as their differences, and what went wrong for them.
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How Do These Two Companies Approach Multi-GPU Setup?
AMD and Nvidia seem to be locked into an eternal struggle for supremacy in the GPU world and although the green team was the first to hit the market with their SLI technology, team red wasn’t lagging too far behind.
Both companies were driven by the romantic idea of hooking up two or more graphics cards and getting double, triple, or even more performance. Or they were aware of the snake oil they’ve tried to sell consumers. Either way, it was us, gamers, who truly believed that this promise could be fulfilled.
Although there are certain games out there where an increase in performance is noticeable or even doubled in some rare cases, it’s clear that neither AMD nor Nvidia truly realized the potential of a multi-GPU setup.
Trying to execute on the same idea was always bound to have things done similarly, and this example is no exception.
Both technologies work in two modes – alternate frame rendering or AFR and split frame rendering or SFR. They both essentially split the load but in different ways.
AFR will have one GPU render every odd frame and the other render every even frame. SFR, on the other hand, will split the frame in half and have one GPU work on the upper part of the frame and the other on the lower part of the frame.
Maybe a little comically, but both technologies have struggled in actually improving the performance and in some instances have actually made the performance even worse.
Another thing that regularly plagues both Crossfire and SLI is a phenomenon called micro stuttering. Basically, when using the multi-GPU set up in your PC with AFR, what you perceive on your screen may be different from what the benchmarking software is showing. Unfortunately, you won’t experience extra frames, quite the opposite, you will experience really annoying stuttering.
Both technologies need a PSU capable of supplying enough power to the GPUs with combinations such as 6-pin, 8-pin, and 16-pin being readily available in the vast majority of modern PSUs.
Another thing these two have in common is that they can run on several monitors and in different resolutions. Although they both can run four 8K or eight 4K monitors. However, the downside is that every monitor will require its own dedicated GPU.
The key difference and probably the most noticeable on a glance is Crossfire’s ability to connect GPUs with the same architecture, while SLI needs two identical cards in order to run.
So a GPU from the HD 5800 series can be combined with another 5800 series GPU (say 5830 and 5870), but a different hundred series can not (so a 5770 and 5870 are incompatible). There is an exception with the HD 7870 XT cards that can be paired up with an HD 7900 series GPU.
A small caveat here should be that SLI cards don’t need to be precisely identical. They can be from different manufacturers. So EVGA GTX 1080 Ti can connect with ASUS GTX 1080 Ti, but neither could connect to any card maker’s plain GTX 1080.
This next thing is both a similarity and a difference, depending on your perspective.
When Crossfire was originally released in 2005, the two cards required a specific bridge to connect, like SLI. However, since 2013, AMD’s Crossfire no longer requires said bridge, and the connected GPUs can communicate directly via the PCI Express bus.
Another factor that gives AMD an advantage is that Nvidia requires the motherboard manufacturers to have a specific certification for SLI, whereas a lot more motherboards can run Crossfire without issues.
However, it’s not all sunshine and daisies for AMD. Their Crossfire’s biggest issue is that it needs external support for games when running in borderless or windowed mode, although fullscreen is fine.
Is There Anything Good About These Technologies?
It would be dishonest if we insisted on being pedantic when it comes to Crossfire and SLI, and their fulfillment of those implicit promises. Sure, neither actually delivered the 100% FPS increase, but maybe we set the bar too high and should, instead, cut them some slack.
The fact is that most of the time, multi-GPU can actually deliver an increase in performance and have a lower frame rate. The biggest pitfall of this technology lies in what was accentuated in the previous sentence.
As spoken earlier, multi-GPU setups are prone to the micro stuttering and due to the lack of general game developers’ support, way too many times the frame rate increase will be negligible or worse, lower.
One could argue that two cheaper GPUs can significantly outperform a single and more expensive card while costing only slightly more. On a surface level, this would appear true and hard to refute.
However, GPUs run at high temperatures, and having two inside your case will only increase its internal temperature. Furthermore, you’ll likely have to upgrade your PSU in order to sufficiently supply your biggest power spenders. Not to mention that if you’re trying to run SLI, you’ll need to have a needlessly more expensive “SLI certified” motherboard.
Should You Get A Multi-GPU Setup?
As always, these decisions will come to your personal preference. However, it’s of utmost importance to say that only in the most extreme case will you ever need more than one graphics card.
As far as Crossfire and SLI go, we all need to accept that these things just aren’t doing it anymore and we have to wonder if they actually worked in the first place.
Most modern games will be just fine with a top of the line GPU and getting two cheaper ones for around the same amount of money to get lesser results just doesn’t sound rational. While judging NVLink already by the sins of its fathers may be too harsh, but it’s been out since 2016 and we still haven’t seen a glimpse of its potential.
In the end, probably the only reason why you should get two or more graphics cards connected is if you’re truly enthusiastic about the tech and want to game at 4K and 144+ FPS (provided you have the monitor for it). Although the latter may not even be possible anymore with either SLI or Crossfire due to the decreasing support from developers following the releases of DirectX 12 and Vulkan.