SLI vs CrossFire – Multi-GPU configurations – Are they worth it in 2021?

Would you like to know what the differences between AMD CrossFire and NVIDIA SLI are? These technologies have become obsolete, but there are now even better ones.

Due to the fact that nowadays modern games heavily rely on GPUs for running properly, gamers will require a powerful graphics card in order to run their favorite games at higher settings.

Today’s gaming cards have graphics processing power that is eminently necessary to play today’s top games at the highest resolutions (1440P, 4K, and beyond).

AMD and NVIDIA both offer SLI and CrossFire configurations to combine up to 2-4 of their GPUs into a single system to boost GPU power. Is that a practical way of making GPUs more powerful?

With this article, we go over how CrossFire and SLI operate and the differences between them, as well as possible pitfalls when using multiple graphics cards.

What Is AMD CrossFire?

As we have recently established, CrossFire is AMD’s proprietary hardware technology for networked graphics that allows multiple AMD graphics cards to synch together for improved graphics quality and performance.

What Is Nvidia SLI?

Simply stated, SLI is the Nvidia equivalent of CrossFire but is exclusive to GPUs from the Nvidia brand. The current implementation of SLI dates back to 2004; however, the underpinning hardware and technology have evolved considerably over time.

SLI and CrossFire, How do They work?

Neither SLI nor CrossFire accomplishes the same thing: they enable a system to divide the processing load among its graphics cards.

It makes sense that having multiple graphics cards split up the burden of rendering frames would mean a faster system, but as we’ll see later, a two-GPU setup doesn’t scale as linearly as it suggests and can sometimes perform worse.

But first, let’s take a look at the difference between SLI and CrossFire before discussing the pitfalls of multi-GPU configurations.

SLI and CrossFire, How do They work?

In fact, both technologies enable you to utilize multi-graphics cards in the same system. NVIDIA has a multi-GPU solution called CrossFire, while AMD has its own multi-GPU solution called SLI.

In addition, both technologies have two operating modes:

1. Split frame rendering: In general, the GPUs split up the tasks of processing each frame. So, one GPU will process one “portion” of the frame, while the second GPU is working on the remaining portion.
2. Alternate frame rendering: There are two GPUs per video card. GPU 1 takes care of frames 1,3,5, and so on, whereas GPU 2 takes care of frames 2,4,6..so on

Differences Between AMD CrossFire and Nvidia SLI

Nvidia SLI and AMD CrossFire might appear to be the same thing except that they only work with a particular line of GPUs. Upon closer examination, the two approaches diverge.

In general, CrossFire can only be used with GPUs from the same architecture generation; otherwise, the requirements are relatively loose. Different manufacturers, clock speed, and RAM aren’t issues.

In comparison, SLI is restricted by the requirements of matching graphics processors of two different manufacturers, not necessarily from the same manufacturer (at MSI and EVGA, for example) and with the same RAM configuration.

As an example, a Radeon RX 570 can be paired with an AMD Radeon RX 580, while a second GTX 1080 card is required for SLI.

While Nvidia maintains perfect performance and consistency through limiting compatibility, AMD offers more diversity and choices, resulting in an outstanding user experience.

Regardless of the model, generation, RAM, or whether you intend to use Crossfire or SLI, combining an Nvidia GPU with an AMD GPU in a multi-GPU setup will not work.

Both AMD Bridge Interconnect and Nvidia SLI Bridge used to be needed in the past, although since the 200 series onward, CrossFire uses the PCIe bus instead.

AMD achieves this by opening a direct channel between GPUs with its hardware engine tech called XDMA.

XDMA eliminates the processor from the discussion between GPUs, as well as any other non-essential parts.

Through Bridge Interconnect, the performance of AMD GPUs does not increase, and the bandwidth they provide is greater than through the current generation.

Although Nvidia has not yet implemented its own solution, it is probably afraid upcoming GPUs will surpass PCIe bus capacity, causing performance issues.

As a result, newer SLI Bridges such as the SLI High-Bandwidth and the NVLink have featured throughout the years. A bridge technology called NVLink offers over five times as much bandwidth as SLI HB and is not available on anything less than a high end RTX 2080 card.

One other difference is that AMD calls Hybrid Graphics, formerly known as Hybrid Crossfire and Hybrid CrossFireX, Hybrid CrossFirex when it works with APUs (integrated graphics units in processors) and discrete graphics cards.

A laptop with a discrete GPU and integrated graphics unit will be able to take advantage of the higher resolutions while also reducing its power consumption.

Both cards perform better for graphically demanding tasks, while less power is used for low-end tasks like browsing the web.

CrossFire makes use of more advanced render techniques – covered in the document below – such as SuperTiling, which splits a frame up into tiles in a checkerboard grid and alternates between those tiles for efficient rendering.

Further differences in performance involve technicalities. Nvidia requires that motherboards be SLI-compliant, which means manufacturers must pay a license fee, as well as PCIe slots to meet a set of specifications.

On the other hand, CrossFire compatibility is much less restrictive, and all that is needed is two PCI slots. For this reason, CrossFire capable motherboards are much less expensive and more readily available.

SLI is more flexible with compatibility in windowed/borderless mode because it works in fullscreen mode unless the developer has engineered it to work in fullscreen mode.

While the above points aside, the biggest difference between CrossFire and SLI is the shift from AMD to the term ‘’mGPU support’’ (multi-GPU support) for CrossFire while Nvidia has continued to use the SLI acronym.

AMD’s rationale is that DirectX 12, which includes multiple GPU support, has changed the way games are played.

It was AMD’s responsibility to create profiles for CrossFire games with corresponding AMD drivers. In other words, to devise drivers tailored to a specific game’s needs.

As opposed to DirectX 12, which shifts the responsibility to the developers, DirectX 12 now requires clear instructions for the developers on how to implement mGPU support into their game engines.

AMD continues to maintain support for DirectX 11-enabled games, including profiles, even though CrossFire has officially been stopped by AMD.

A slow process is required in order to transition to DirectX 12 games and engines, therefore AMD support is expected to continue for the foreseeable future.

The similarities between AMD CrossFire and Nvidia’s SLI

There are some differences, but the idea is the same; in fact, there are significant similarities.

SFR and AFR are two rendering modes CrossFire and Nvidia share for cross-GPUs. SFR splits the frame into two parts. The work is split and rendered separately before combining the result to create a single frame.

The CrossFire setup uses the Scissor mode rather than SFR but the process is the same.

Alternate Frame Rendering (AFR) assigns specific frames to each GPU on an alternate basis, so the first frame is rendered by the GPU on one side, the next frame by the other, and so on.

CrossFire and SLI are both compatible with dual, triple, and quadruple GPU setups. Additionally, they work best when combined at higher resolutions for graphically intensive games.

Despite the fact that both technologies have essentially the same characteristics, they are criticized differently regardless of their execution. The main complaint is the need for pre-configured profiles from AMD and Nvidia, which will hopefully change as DirectX 12 becomes more mainstream.

Further, it is widely recognized that AFR mode stutters as well as CrossFire and SLI.

Conclusion

The popularity of multiple GPUs in overall gaming hardware is on the decline, despite the fact that understanding their fundamental differences between AMD CrossFire and Nvidia SLI can be extremely useful.

Most games can be run on a single GPU with some wiggle room, meaning that dual GPUs are not an advantage.

These GPUs are now so powerful that buying more of them is prohibitive. As a result, only hardcore enthusiasts interested in extremely high-resolution gaming will need multiple GPU setups.

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