At one point, a few years ago, if you wanted to make the most out of a gaming PC, you needed multiple graphics cards in a multi-GPU setup. This became possible when Nvidia introduced SLI, and AMD introduced CrossFire. Both technologies had the same goal – allow you to harvest the power of multiple GPUs to get the best performance possible.
However, as GPUs become increasingly more powerful, we don’t see multi-GPU setups all that much anymore. They’re used a lot more often in professional settings such as rendering machines or farms, but for gaming, not really.
With that in mind, let’s take a look at what multi-GPU setups are. We’ll also see how they work, and whether or not you should be considering them today.
In its simplest form, a multi-GPU setup splits up the frame processing workload on multiple graphics cards, allowing your whole system to render the frames more quickly. The technical explanation is a bit more complex than this, but this is pretty much all you need to know – more GPUs allow you to render more frames at the same time.
It’s worth noting, however, that the performance scaling is not linear. For example, if you get 50 frames per second with a single GPU, adding another identical one will rarely get you 100 frames per second. To make matters more interesting, adding a third, or even fourth GPU, nets you an even smaller performance increase.
With that out of the way, let’s take a look at the two multi-GPU solutions you have available at the moment, which are Nvidia’s SLI (and NVLink), and AMD’s CrossFireX.
Even though both solutions have the same goal, they work in a slightly different manner. There are some common things about both and some major differences that may sway your decision towards one or the other. Let’s kick things off with the similarities.
Both SLI and CrossFireX can operate in split frame rendering or alternate frame rendering. Split frame rendering allows the GPUs to split the workload of processing a single frame, where one of the GPUs renders one part of the frame, and the other one picks up the rest. On the other hand, alternate frame rendering means that one GPU will render the current frame, while the other GPU takes the next one. For example, you’ll have the first one render frames 1, 3, 5, 7, and so on, while the second GPU picks up 2, 4, 6, 8, etc. You get the point.
Now, to the differences. SLI is a bit more “premium” feeling in a few ways. First, an SLI, or NVLink configuration, will cost you more. This is because Nvidia requires motherboard manufacturers to pay to have their motherboards be SLI certified. And because of this, you’re oftentimes limited to premium motherboards. AMD doesn’t require any certification, and even a lot of current budget motherboards can run CrossFire.
Furthermore, SLI requires that you use identical GPU SKUs. While you can SLI an ASUS RTX 2080 with an MSI RTX 2080, you still must have two RTX 2080 graphics cards – even if they’re made by a different partner brand. With CrossFire, you can use different GPUs, as long as they’re using the same architecture. For example, an R9 390 can be used in CrossFire with an R9 380, because they’re made on the same architecture. In this case, the performance of the R9 390 will be lowered to that of the R9 380. But you can’t pair an R9 390 with something like an RX 570, for example.
And last but not least, there’s the connectivity method. With Nvidia’s SLI and NVLink, you need a physical bridge that connects both GPUs. While this is not too expensive in most cases, it’s still an extra purchase. AMD’s CrossFire uses the PCIe 3.0 lanes to allow both GPUs to communicate with each other.
Well, there’s only one – performance. Even though today’s modern GPUs like the RTX 2080 Ti, or the RX 5700 XT, are rather powerful, sometimes you just need a bit more power. Of course, this is usually in extreme situations, such as high framerate 4K gaming, especially with demanding titles. But if that’s the case, multi-GPU setups are the only thing that can get you the performance you need. Well, at least until we get new GPUs that are more powerful and handle 4K easily.
But even with performance, as we mentioned, you don’t get linear scaling. You might, with certain titles that are well optimized for multiple GPUs, but in most cases, you’re looking at a 50-70% increase in performance when you add a second GPU. And adding even more GPUs nets you an even smaller increase in performance.
Yes, a few, and they’re the reason why multi-GPU setups aren’t all that popular nowadays. The first one is cost. Whether you go for Nvidia or AMD, you need to buy a second (and maybe third, and fourth) GPU. With higher-end GPUs, this becomes a costly solution rather quickly. If you opt for an Nvidia GPU, there’s also the requirement for a higher-end, certified motherboard, too.
Next up, you have power, which is somewhat connected to cost as well. More GPUs will require a lot more power to drive. And as some of the most demanding components in a system, you will very likely need to get a powerful PSU. Depending on the graphics cards you’re going for, you may need to go for something powerful, like a 1200W or even a 1600W power supply. These power supplies are expensive, and of course, they’ll also reflect on your electricity bill, too.
Then there are the temperatures. GPUs tend to emit a lot of heat when they’re under load, and you need to have good cooling to keep the temperatures at bay. With multiple GPUs, this is increasingly more difficult with air cooling. The GPUs are close to each other, which restricts airflow. Yes, you could go with liquid-cooled GPUs or even a custom water cooling loop, but that’s pretty expensive.
Last but not least, you have driver issues. There’s no denying that multi-GPU setups never actually worked as well as they should’ve. There were (and still are) issues with the drivers from both AMD and Nvidia, and there were the issues of games not being well optimized. Remember when we mentioned you don’t get double the performance with a second GPU? Well, bad driver and game optimization reduced those gains even further, making multi-GPU setups an even worse choice.
At this point, you’re probably wondering why you would even look at multi-GPU setups with all these downsides. But there’s still one situation where SLI and CrossFireX make sense.
With all the things we mentioned, the one situation where a multi-GPU setup makes sense is when money is no object. If you want the absolute best performance you can get, pairing two (or three, or four) high-end graphics cards is your only solution.
Now, yes, that will cost a lot. The powerful and high-quality power supply will cost a lot, too. You will need a motherboard with enough PCIe slots for the graphics cards you intend to use – that costs a lot as well. Did we mention you will need a large case with plenty of airflows, and potentially a custom water cooling loop? Yes, it gets very expensive, very quickly.
At the end of the day, both SLI (and NVLink) and CrossFireX only make sense if you’ve got an insane setup with multiple 4K monitors, or something other that’s just as extreme.
There is another scenario that may be worth mentioning, but it’s not for everyone. If you already have a system with an older, but higher-end GPU, and a motherboard that supports a multi-GPU setup, you could be better off buying another identical GPU, used, instead of replacing it with a modern one. This is a very specific scenario because it’s not always worth it, but one you could consider.
Nowadays, as we mentioned, things aren’t all that exciting as they were a few years ago. This is mostly because modern high-end GPUs can get you pretty great performance in many scenarios. For example, any high-end GPU can handle high framerate 1080p gaming with ease.
To add to this, developers nowadays don’t optimize games for multi-GPU setups like they did a few years ago. This, paired with the fact that drivers didn’t really get any better for multi-GPU setups, makes such a setup difficult to recommend.
The short answer would be no. However, as we mentioned, there are some situations where it actually might be a good idea. If you’re in one of the situations we mentioned earlier, yes, by all means, go for it. But for everyone else, you’re much better off investing your money in a good single GPU setup.