Getting two or more graphics cards to do one single job sounds like an amazing idea in theory, but it might not yield such extraordinary results. There were a host of issues that plagued both AMD’s Crossfire and Nvidia’s SLI. Despite both of them being valid approaches to the multi-GPU tech, 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 these companies offered for their respective multi-GPU solution would unfortunately continue throughout their entire lifespans.
Crossfire was officially put to sleep in 2017. SLI, despite technically still having a pulse, has now been replaced by NVLink, depending on who you ask. Nevertheless, it’s still true that Nvidia’s SLI upgrade does offer a massive enhancement.
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 gaming enthusiasts found valuable enough to use.
Still, the very idea of it is fascinating. Now 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 in an eternal struggle for supremacy in the GPU world. 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 doubling or tripling 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.
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.
As we’ve pointed out, both technologies have struggled to actually improve the performance and in some cases they have actually contributed to its detriment.
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. This might lead to some good old 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. They can also both 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 only 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 cannot (so a 5770 and 5870 are incompatible). There is an exception with the HD 7870 XT cards, which can be paired up with an HD 7900 series GPU.
A small caveat here is 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 this 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 fulfilment of those implicit promises. Sure, neither actually delivered the 100% FPS increase, but maybe we set the bar too high.
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 mentioned earlier, multi-GPU setups are likely to cause micro stuttering and, due to the lack of general game developers’ support, more often than not 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 need 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, this decision should be based on your personal preference. However, it’s of utmost importance to say that only in very extreme cases 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 admit that maybe they didn’t even work 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 doesn’t make any sense. While judging NVLink by the sins of its fathers may be too harsh, 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 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). However, remember the latter may not even be possible anymore with SLI or Crossfire due to the decreasing support from developers following the releases of DirectX 12 and Vulkan.