There are two terms that you’ve probably heard of when it comes to multi-GPU setups: CrossFire and SLI. AMD and Nvidia created these technologies, which allow two or more GPUs to work together.
If you’re considering purchasing numerous graphics cards, keep reading to learn more about the similarities and differences between these two technologies.
What Is AMD CrossFire?
CrossFire is the name of AMD’s patented hardware technology that allows two or more compatible AMD GPUs to operate together, thus enhancing graphics quality and performance, as we’ve already established.
What Is Nvidia SLI?
SLI is essentially Nvidia’s version of CrossFire, only it only works with Nvidia GPUs. It has been around since 2004, although the underlying hardware and technologies have changed greatly since then. SLI is still around today.
Differences Between AMD CrossFire and Nvidia SLI
Although they appear to be the same technology, AMD CrossFire and Nvidia SLI are really implemented differently. We see a difference between the two techs when we dig deeper into the details.
Crucial to CrossFire is that it only works with GPUs that are part of the same architectural generation. It doesn’t matter if the clock speed, the RAM, or the manufacturer is different.
Compared to this, SLI has more stringent requirements, such as two identical graphics processors (with varying clock speeds to allow for overclocking), from different manufacturers (such as MSI or EVGA) and with similar RAM configurations.
CrossFire, on the other hand, allows the pairing of two AMD Radeon RX 580 graphics cards with no complications, whereas SLI requires two Nvidia GeForce GTX 1080 graphics cards.
Nvidia focuses on limiting compatibility to guarantee a consistent user experience, whereas AMD offers a wide range of alternatives and flexibility, which results in a less consistent user experience.
At this point, if there is any uncertainty at all, a multi-GPU system with an Nvidia and an AMD GPUs won’t work, no matter how old they are and no matter how much RAM they have.
In the past, both AMD Bridge Interconnect and Nvidia SLI Bridge were necessary for CrossFire, but from the 200 series, CrossFire makes use of the PCIe bus instead of a bridge.
By using XDMA, AMD opens up a direct connection between the GPUs and is capable of doing so.
XDMA eliminates the need for the processor and any other GPU components that aren’t absolutely necessary in order to communicate between two GPUs.
When using AMD GPUs, performance is unaffected and bandwidth is more considerable than when using the Bridge Interconnect.
Perhaps worried about the PCIe bus maxing out and causing performance concerns, Nvidia has yet to implement a similar approach.
Rather, the SLI Bridge technology has been improved over time, moving from Standard SLI to SLI HB and then to NVLink. There is a bridge technology that offers 50 times the bandwidth of SLI HB and is only available with RTX 2080 cards.
AMD’s Hybrid Graphics, previously known as Hybrid Crossfire and Hybrid CrossFireX, is a major distinction between CrossFire and its predecessors, which worked only with standalone graphics cards.
Lower-tier cards and laptops with integrated graphics and a separate GPU can benefit from this technology, which aims to improve the machine’s graphical capabilities while reducing power consumption.
Both graphics cards work together to provide greater performance for tasks that require a lot of power, such as web browsing.
CrossFire employs a method known as “SuperTiling,” which breaks each frame into pixel tiles arranged in a checkerboard pattern. The rendering of the grid tiles is subsequently distributed among the GPUs in this manner.
Then there’s the small matter of specifics. To be SLI certified, motherboards must be licensed by Nvidia, and the PCIe slots must meet a set of standards.
CrossFire compatibility, on the other hand, requires only two PCIe slots on a motherboard. Because of this, CrossFire-enabled motherboards are more commonly accessible and at a significantly reduced price.
Compared to SLI, CrossFire can only be used in fullscreen mode unless specifically developed by the developers, whereas SLI can be used in windowed or borderless modes.
There are a few minor differences between CrossFire and SLI, however AMD dropped the brand name for “mGPU support” (multi-GPU) towards the end of 2017 in favor of the SLI abbreviation.
The reasoning behind AMD’s decision is that the way a game supports multiple GPUs has radically altered since the introduction of DirectX 12.
With DirectX 11, AMD had to take the lead in creating game profiles. To put it another way, CrossFire-optimized drivers for their cards.
DirectX 12, on the other hand, places the onus on the developers to implement mGPU support in their game engines and provide specific guidance on how to make advantage of the dual (or more) GPUs.
AMD continues to support DirectX 11 games and produce profiles, despite the fact that CrossFire has been officially and honorably retired.
DirectX 12 is still a long way off, thus AMD’s support will likely be around for a while.
Similarities Between AMD CrossFire And Nvidia SLI
The underlying principle is the same, and as you might think, there is a lot of overlap between the two.
SFR and AFR are the multi-GPU rendering modes shared by CrossFire and Nvidia. split-frame rendering is a technique that allows two or more cards to be rendered independently of each other in a single frame. A single frame is created by combining all of the rendering effort.
The mode is known as Scissor rather than SFR in a CrossFire setup, but the mechanism is the same.
When using Alternate Frame Rendering (AFR) or Alternate Frame Assignment, each card is assigned a different frame. The initial frame is drawn by one GPU, while the next frame is drawn by the other.
CrossFire and SLI both enable two, triple, and quadruple GPU configurations. Both technologies are best suited to high-quality games that require high resolutions.
The essential premise of both technologies is the same, hence the amount of criticism is about the same. However, as DirectX 12 makes advances in the months and years to come, the most often berated issue is the requirement for profiles from AMD and Nvidia for games to operate.
The AFR mode for both CrossFire and SLI is commonly acknowledged to have micro-stuttering issues.
A Primer on How They Work and the Differences Between Them
Using multiple graphics cards in SLI or CrossFire allows a computer to distribute the processing of graphics-related data among them.
It is theoretically possible to render frames more quickly if you have many graphics cards split up the job of processing the frames. However, the performance of multi-GPU configurations does not scale linearly (although, in certain games, dual GPUs can produce a near doubling of performance in terms of average framerate).
To begin with, let’s look at the benefits and drawbacks of using multiple GPUs in SLI and CrossFire.
To begin, NVIDIA offers SLI, whilst AMD has CrossFire, both of which are multi-GPU solutions. Both allow you to run many graphics cards in the same system, which is a similarity between the two technologies.
There are two modes of operation for each of these technologies:
- In a nutshell, the GPUs divide up the computational load for each frame. This means that one GPU will focus on a “part” of the frame, while the other GPU will focus on the rest.
- Work is distributed over a set number of GPUs, each of which renders a different frame at the same time. Frames 1,3,5, and so on will be handled by GPU 1, whereas frames 2,4,6 will be handled by GPU 2.
There are, however, a few key points to keep in mind:
- A GTX 1080 can only be SLI’d with a separate GTX 1080, but the brand of the card does not matter. Unlike SLI, which requires the usage of identical GPUs, CrossFire works with different GPUs of the same architecture (an RX 580 can be CrossFired with an RX 570, but not with an R9 390)
- SLI requires the use of a cable or SLI bridge to link the two cards. PCIe 3.0 has replaced PCIe 2.0 as a means of interconnecting AMD CrossFire cards, which previously required a direct connection between the cards.
- In general, SLI setups are more expensive than CrossFire setups because NVIDIA needs motherboard makers to pay to be “SLI” certified, whereas AMD does not require any certification and, as a result, there are many more motherboards that enable CrossFire, including budget-friendly ones.
The Pitfalls of Using Multiple Graphics Cards
However, in recent years, the performance benefit of running SLI or CrossFire systems has reduced slightly. Utilizing multiple graphics cards has been an excellent way for consumers to obtain more in-game performance out of their PCs.
Multi-GPU compatibility was more common in the past, however this is no longer the case. Developers are now less concerned with optimizing their games for SLI and CrossFire systems than they were in the past.
But twin GPUs can still deliver a nice boost, with several benchmarks showing 50% greater increases when a second card is added.
There are still questions about the future of dual-GPU configurations. Even NVIDIA has reduced support for SLI on a couple of their most recent generation cards. To use SLI, you must have at least a GTX 1070 or higher. NVIDIA does not officially support the GTX 1060 in multi-GPU systems, however it is possible to do so (they have not included the SLI connection ports on 1060s).
Additionally, running SLI or CrossFire systems can be prohibitively expensive for anyone with any type of budgetary restraints.
A single GTX 1080 Ti costs about the same as a pair of GTX 1070s, thus one could argue that the price-to-performance of the two cards is comparable or even better than the performance of a single 1080 Ti. Dual GTX 1070s, on the other hand, necessitate a more expensive power supply, motherboard, and case/cooling. The reason for this is that using two graphics cards will result in higher power and heat consumption, as well as the need for a SLI-certified motherboard, all of which can be quite expensive.
Split frame rendering and alternate frame rendering (AFR) are the two modes of operation for both technologies (SFR). In essence, both of them divided the work, but they did so in quite distinct ways.
Every odd frame will be rendered by one GPU, and every even frame by the other, thanks to AFR’s intelligent scheduling. On the other hand, SFR divides each frame in half and uses two GPUs, one for processing and the other for rendering, to handle the upper and lower portions of each frame, respectively.
Graphical performance has been hampered by both of these technologies, as previously indicated. In fact, they may have contributed to its degradation in some circumstances.
Both Crossfire and SLI suffer from a problem known as micro stuttering. It’s possible that what you see on your screen and the results from your benchmarking program disagree when you’re running AFR on a PC with multiple GPUs. Stuttering may ensue as a result of this.
PSUs that can deliver enough power to the GPUs are required for both technologies, and the vast majority of modern PSUs come equipped with combinations such as 6-pin, 8-pin, and 16-pin.
They both have the ability to run on many monitors and in a variety of resolutions. Both have the ability to run four 8K or eight 4K displays at once. Each monitor will need its own dedicated GPU, which is a drawback.
Crossfire may connect GPUs with different architectures, whereas SLI needs two identical cards to work. This is the most notable distinction at first glance.
To put it another way, the 5830 and 5870 are examples of two GPUs from the HD 5800 series that can be used in conjunction with one another (so a 5770 and 5870 are incompatible). Exceptions to this rule exist in the form of the HD 7870 XT cards, which can be used with an HD 7900 series graphics card.
One thing to keep in mind is that the SLI cards do not have to be identical in every way. They can be made by a variety of companies. Even while both the ASUS and the EVGA cards are capable of connecting to one other, they are not capable of connecting to a normal 1080.
To connect the two GPUs in Crossfire back in 2005, a special bridge was required, as was the case with SLI. AMD’s Crossfire, introduced in 2013, does away with the need for a bridge entirely, allowing the GPUs to interact directly over the PCI Express bus.
While NVIDIA’s SLI requires motherboard manufacturers to be certified, AMD’s Crossfire is compatible with significantly more motherboards, giving AMD an advantage over NVIDIA.
AMD, on the other hand, can’t celebrate just yet. The greatest problem with the Crossfire is that it requires external assistance for games while operating in borderless or windowed mode, however fullscreen works fine.
Are SLI or CrossFire Right for You?
As we’ve seen, SLI/CrossFire have their advantages and disadvantages. We’ve also discussed how they function, when they’re most useful, and what to watch out for.
SLI and CrossFire don’t make a lot of sense for the vast majority of gamers. If you’re playing on a 1080P or 1440P panel, running several graphics cards generally isn’t worth the hassle. But if you’re trying to run games at their highest settings on a 4K or 1440P 144Hz monitor, you might benefit from adding a second graphics card.
When Do Multi-GPU Configurations Make Sense?
With SLI and CrossFire, customers can obtain greater performance in situations where a single-GPU solution isn’t powerful enough.
To put it another way: trying to run a 1440p 144Hz (or higher) game at its highest settings on a 144FPS 1440p monitor today. Alternatively, you may try running games on three 4K monitors. Or, for that matter, any other extreme cases.
Some extreme use cases, such as 4K gaming on a 1440P 144Hz panel, require graphics cards like the GTX 1080 Ti and GTX 1080, which are capable of handling most games at high settings on a 1440P 144Hz monitor.
As a result, many GPU configurations are needed. No, you won’t get a performance bump four times as large as running the identical card on its own (at least across the board). A 4K or 1440P 144Hz monitor is a must if you want to play games at their highest settings and framerates, but even if you don’t, you’re probably dealing with a pretty high budget nevertheless. For certain cases, a second (or third or fourth) graphics card is probably not out of the question if you have the spare cash lying around.
An alternative to upgrading an outdated graphics card to a higher-end single GPU is to use a multi-GPU arrangement when you have a superior price-to-performance ratio by adding a second card.
To put it another way, if you have a GTX 970 and are trying to get more in-game performance out of your system, you could be better off picking up a second GTX 970 for around $175 (used) on eBay and that should give you a nice performance gain in the games that utilize SLI correctly. If you want to replace your GTX 970 with a GTX 1070, you’ll have to fork over at least $400 right now, which isn’t a massive upgrade when you consider that the GTX 970 is still quite new.
Going multi-GPU is a viable option if you want to build an extreme gaming PC that can run games with the highest settings and framerates possible on high-resolution monitors with quicker refresh rates.
Multi-GPU systems are no longer as common as they once were, despite the fact that it’s important to know the distinctions between AMD CrossFire and Nvidia SLI. Even if you don’t care about it, it’s become a niche interest in gaming hardware.
Because even the most demanding single-GPU games can be handled by powerful single GPUs, the advantage of using two GPUs is essentially nonexistent.
Since contemporary GPUs are so expensive, purchasing more than one is out of the question. There is no longer a requirement for multi-GPU configurations save for diehard enthusiasts who want to run exceptionally high resolutions.
Another stuck in the wheel of multiple GPU adoption may be AMD handing over compatibility for DirectX 12 games to developers. Nvidia, on the other hand, is reserving the use of SLI for its most expensive models, such as the 2080 cards, and making it less and less common in newer series.