Previous technologies, such as PCI and AGP , used separate buses, which did not allow graphics cards to be bridged together. The PCI Express slots must also support enough bandwidth for the cards, which typically means they must be x8 or x16 slots.
Of course, the cards themselves must also support SLI bridging in order to work together. If you would like to reference this page or cite this definition, you can use the green citation links above. The goal of TechTerms. We strive for simplicity and accuracy with every definition we publish. Ultimately, Nvidia seems to be slowly phasing out SLI support as it ships newer models, which is the best sign that the technology is on the decline.
The price of these models means the likelihood of anyone beyond power users using the tech is unlikely. As more and more developers migrate towards the newer and more versatile version of the omnipresent API, the possibility of titles supporting SLI plummets in parallel. SLI devotees claim otherwise. However, there is the distinct sense that after funneling thousands upon thousands of dollars into a top of the range dual GPU setup, this group is eager to justify their investment with a brash and hearty dose of cognitive dissonance.
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Samuel closely follows the latest trends in the gaming industry in order to keep the visitors in the flow. You Might Like These Too. This is not so straightforward, however; because we can define hardware boundedness purely by which subsystem we're waiting on the longest - be it only a few milliconds or a few dozen - scaling isn't exactly predictable or consistent within even a single area of one game because rendering conditions can change very rapidly, but as we'll see in a moment, there is another side to bottlenecking that can be born from multi-GPU systems.
If we were to massively simplify the process of creating a frame in an 2-Way SLI system then measure how long each component took to complete its share of the work, it might look like one of the images below. These representations may seem extreme, but they aren't unrealistic. To the left we see a 2-Way SLI system that is completely restricted by the CPU, and because the GPU finishes its work so much faster than the CPU, there is absolutely no performance gain to be seen with the addition of a second graphics card.
On the right we see that each of our GPUs take far longer than the CPU to render, and the presence of a second graphics card has effectively doubled the frame rate. The CPU even has enough downtime to accommodate a third graphics card for better performance!
As stated before, however, this isn't how things will look all of the time. If we want to see more use out of our second graphics card, that means we have some tweaking to do.
Neither component would necessarily be limiting the other and we get to see the full benefit of our second GPU. Regardless of how many GPUs we're trying to manage, the takeaway message should be that this isn't necessarily a bad position we're in.
That GPU downtime means we have the ability to increase our game's image quality at a lower cost to our frame rate or perhaps no cost at all, and if we were to keep pushing forward with that idea, we'd be able to force our GPUs to become the system bottleneck and further improve our GPU scaling.
We could try overclocking our CPU in order to try and reduce that GPU idle time, however this is only good up to a certain point, and it isn't necessarily an option for everyone in the first place.
Some much simpler options include increasing the game's resolution playing on multiple monitors, for example, increasing graphics settings or enabling new ones ambient occlusion, antialiasing, depth-of-field, draw distance, field of view, HDR, lighting effects, motion blurring, PhysX, reflections, shadow quality, tessellation, texture quality, etc.
All of these options will not only make our game look better, but it will also increase the GPU render time which can translate to better performance scaling. Now that we're familiar with what SLI is and what it does, let's look at what we'll need to use it. There are three key areas we'll have to focus on: the graphics card, the motherboard, and the power supply. There are also very few restrictions regarding what GPUs can be grouped together in SLI: only the model and memory amounts have to match.
For example, a GTX with 1. Beyond that, manufacturers can be mixed e. Below is a chart with modern retail SLI-ready GeForce graphics cards, all of which are at least capable of 2-way SLI; specially marked GPUs can run in configurations of 3-way or 4-way SLI when proper requirements motherboard, power supply, operating system are met. Check out the complete list at GeForce. It's worth noting that in the case of pairing graphics cards with discrepant clock speeds, the driver will not attempt to synchronize their frequencies unless you instruct it to through tools like EVGA Precision or MSI Afterburner.
Should you choose to run the cards with asynchronous clocks, it's recommended the faster GPU is installed as the primary so single-GPU or low-scaling applications can benefit from its slight performance advantage. There's not much left except to start using SLI and begin fine-tuning our system for optimal performance and image quality. There is technically no "proper" orientation for the 2-way bridge, and if two cards running in SLI have two goldfinger ports indicating support for 3-way SLI the bridge does not need to be installed on a particular set; two separate 2-way bridges may be used as well, but this would be purely aesthetic as no performance gains would be earned.
When this link is not present the PCIe bus will become the means of communication, which can degrade performance. If you are using multiple monitors, click here for requirements and connection diagrams.
Your screen will blacken and flash, possibly several times while the graphics driver re-configures itself and the GPUs for SLI. Once the desktop returns, you will be asked if you'd like to keep or revert your settings within the next few seconds; if you do not select an option before the time runs out, the drivers will revert to a non-SLI state as a failsafe in case your monitor does not return at the end of the process.
If there is a check beside it, it is enabled. If there is not one, it is disabled. Two white vertical bars will be on the left-hand side of the screen with a green box in the middle. The box will grow in size as SLI scaling increases, so a tall box means excellent GPU scaling while a shorter box indicates more limited performance gains.
The global profile affects how the GPUs will render by default. That is, unless an application profile has been altered to use a certain setting, it will use the global settings ex: if we use 16x anisotropic filtering in the global profile, all games will run with 16x anisotropic filtering.
Application profiles can control visual settings for specific games or applications which override the global settings, permitting finer levels of control for optimum performance and image quality on an individual basis. To decipher the array of options, let's separate the visual settings from the functional ones first. The visual settings can produce observable differences in how an object or surface will look in a game, while functional settings change how the GPU behaves.
The result is more realistic shadows, although this will have the GPUs working noticeably harder to produce the effect. Applications that support ambient occlusion natively may also support for driver-level ambient occlusion, but be careful to only enable one at a time as both AO implementations will be used and overlap each other, costing additional performance and perhaps introducing artifacts.
Secondly, you need identical graphics cards. They need to be the same model and series , although it is possible to get them from different manufacturers. In a two-card setup, the master will work on the upper part of the screen , while the slave will manage the bottom part. Once the slave has rendered its part of the screen, it sends it to the master, which then combines the two renders and outputs to the monitor.
In those rare cases where the cards are mismatched, the slower or lesser card will become dominant, with the better card adjusting by either running at the same speed as the other card or disabling its extra memory.
SLI Bridge connects the graphics cards. This is also possible for high-end cards , though not recommended. This is where SLI Bridge is useful because it reduces the bandwidth constraints and can transfer data directly between the cards.
While the two-GPU setup is likely the most popular one, SLI can also be configured in a three or four GPU dynamic by either using a single bridge that connects every card or by combining two two-way bridges. The future is uncertain for these layouts as NVIDIA is phasing out its support for more than two-card combinations due to high driver complexity.
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