What Is SLI? List Of SLI Compatible Cards

Scalable Link Interface or SLI is the brand name for Nvidia’s multi-GPU technology meant for linking up two or more graphics cards into a single output using a parallel processing algorithm. It sounds like a mouthful, but this is a really cool technology that has also been used by their competitors AMD with their CrossFire brand, and it’s worth talking about.

Let’s see how all of this works!

Fun fact: Nvidia isn’t the innovator of this technology as they acquired it from 3dfx Interactive who introduced it in 1998. At that point, it was a little ahead of its time, but in 2004, when SLI made its reappearance, the market for top-performing gaming equipment was ripe.

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What Is Needed To Run SLI?

Geforce Gtx - Four Way SLI

A friend of mine actually fried his motherboard thinking that just because he had enough slots, he could insert graphics cards and just boot up the computer. Okay, that was me. But still, there are few more requirements than just a couple of open PCI-Express x16 slots. 

First, you must check if the motherboard is SLI compatible. This is a really important one step, so be cautious, especially because there are motherboards that support SLI, or CrossFire, or both, or neither. Of course, if you’re only going for a two-card setup, then cards can be configured to work in SLI mode.

Second, you need identical graphics cards. Hooking up a GTX 1080 and GTX 1070 will not work, despite their similarities. They need to be the same model and series, although it’s possible to get it from a different manufacturer. So for example, if one is made by MSI and the other by Asus, and the third one by Gigabyte, you’ll still be able to configure them together on the same machine.

There is a caveat here. In some extremely rare exceptions, it is possible to run “mixed SLI” configurations on some cards that only have a matching core codename, so G70, G73, G80, and so on.

Another important thing here is that the graphics cards are set up in a master-slave configuration.

Before your mind wanders, this means that one card will be in the role of a “master” despite the workload being distributed equally to all cards. In a two-card setup, the master will work on the upper part of the screen, while the slave will handle the bottom part. When the slave finishes rendering, it’ll send it to the master who will then combine the two renders and output to the monitor.

In those rare cases where the cards are mismatched, the slower or lesser card will become dominant with the better one adjusting by either running at the same speed as the other card or disabling its extra memory.

Geforce Gtx - SLI Connector

SLI Bridge connects the graphics cards. It is also called the SLI Connector as its purpose is to establish a direct connection between the cards. It is possible to run two low-end or mid-range cards without the bridge by using the chipset on the motherboard.

This is also possible for high-end cards, although not recommended as the results will be very poor seeing how the chipset just doesn’t have enough memory. This is where SLI Bridge comes in because it reduces the bandwidth constraints and can send data directly between the cards.

There are three types of SLI Bridges:

  • Standard Bridge (400 Mhz Pixel Clock, 1GB/s bandwidth) – This is a traditional bridge included with motherboards that support SLI up to 1920×1080 and 2560×1440@60 Hz.
  • LED Bridge (540 MHz Pixel Clock) – This one is recommended for monitors up to 2560×1440@120 Hz+ and 4K and is sold by Nvidia, EVGA, MSI, Asus, and a few others. It can only operate on an increased Pixel Clock if the GPU supports that clock.
  • High-Bandwidth Bridge or SLI HB Bridge (650 MHz Pixel Clock and 2GB/s Bandwidth) – This is the fastest bridge and is sold exclusively by Nvidia and is recommended for monitors up to 5K and surround. SLI HB Bridges are available only in 2-way configurations.

While the two-GPU setup might be the most popular one, SLI can also be configured in a three or four GPU dynamic by either a single bridge that connects every card or by combining two two-way bridges. Combining three or four dual cards set up with a 2-way bridge is impossible as the technology for hexa- or octa SLI configuration doesn’t exist.

The future is uncertain for these layouts as Nvidia is phasing out the support for more than two-card combinations due to high driver complexity, and as a matter of fact, cards like GTX 1070 or GTX 1080 and higher only support the two-way SLI.

SLI is supported by all Windows versions following Windows Vista, both 32-bit and 64-bit. It can also be configured to work on Linux, but seeing how there aren’t a lot of high-end graphics video games developed for that platform, it seems futile to even try. 

SLI requires at least 2 GB of RAM for a 32-bit system and 4 GB for 64-bit. Nvidia released NVIDIA ForceWare Unified Driver Architecture (UDA) all the way back in 2003 and it has built-in support for SLI technology. So, there’s no need for additional SLI-specific drivers, but you still need them for each graphics card.

Powerful Power Supply Unit For GPUs

A very powerful and reliable Power Supply Unit is necessary as the GPUs are big power consumers and you’ll be running two or even more at the same time. High-end graphics cards can use up to 200-250 watts of power so beware of this as well.

Important: not all games and applications support SLI. For those that do, Nvidia includes SLI profiles in their driver package so you don’t have to set anything up manually to get far greater gaming experience.

SLI Modes

Split Frame Rendering

SLI Mode - Split Frame Rendering

SFR analyzes the rendered image to divide the load between the GPUs. To achieve this the frame is split on a horizontal line, depending on geometry. For example, if the upper part of the screen is rendering the sky, then this line will be lower in order to balance out the geometry workload on the GPUs.

Alternate Frame Rendering

SLI Mode - Alternate Frame Rendering

AFR means that each frame is rendered by a different GPU. In practice, this is most commonly executed with one card working on odd frames, and the other on even frames. Although AFR might have a better frame rate than SFR, it may cause micro stuttering which changes the way frame rate is perceived. While the frequency at which frames arrive may be doubled, the production time of the frames is not, so this cannot lower the input lag.

SLI Antialiasing

SLI Antialiasing - A New Standalone Rendering Mode

This is a separate rendering mode that can double the antialiasing performance by splitting the workload between the GPUs. One card will perform an antialiasing pattern that is offset to the regular pattern, for example, a little to the right and down, while the other one will do the same thing with an equal offset in the opposite direction, left and up in this example.SLI Antialiasing has some advanced options like SLI 8X, SLI 16X, and SLI 32X, although the last one is only for Quad SLI systems.

Hybrid SLI

This is a generic name for two technologies, GeForce Boost and HybridPower.

GeForce Boost used integrated graphics and a discrete GPU combination to increase performance. On the other hand, HybridPower is not a performance-enhancing mode. It also uses IGP and a GPU on an MXM module which is used to easily integrate the GPU on laptops. As it’s a big power consumer, the MXM module will shut down when the laptop is unplugged from the power supply. This isn’t a laptop only thing as it can also be found in desktop computers.

A very important thing to note is that a high-end SLI setup will require a powerful CPU to prevent bottlenecking.

NVLink – Is This The Death Of SLI?

It would be more accurate to say that the future of multi-GPU setups is in question as the gaming industry still hasn’t fully embraced its advantages. While AMD’s CrossFire appears at the brink of extinction, Nvidia still has a few tricks up its sleeve.

Enter NVLink, a wire-based communications protocol serial multi-lane near-range communication link. And you thought SLI’s definition was a mouthful. Like SLI, it’s a way to connect multiple graphics cards for a single purpose, but a little more spiced up.

So far, it only works in a two-card setup, but that should be enough given its use of NVLink Bridge. Like the SLI Bridges, it connects two cards, but it can provide 10-12 times better link speed.

The extra speed is further accentuated by the fact that NVLink uses mesh networking to communicate instead of a central hub. This means that there is no master-slave relationship going on, and each card can work to its full capacity all the time.

If you’re interested in using multiple GPUs in the SLI setup, here is the list of all NVIDIA desktop GPUs that support SLI.

GeForce RTX 2080 Ti
GeForce RTX 2080 SUPER
GeForce RTX 2080
GeForce RTX 2070 SUPER
Nvidia Titan Xp
GeForce GTX 1080 Ti
Nvidia Titan X
GeForce GTX 1080
GeForce GTX 1070
GeForce GTX TITAN X
GeForce GTX 980 Ti
GeForce GTX 980
GeForce GTX 970
GeForce GTX 960
GeForce GTX 950
GeForce GTX TITAN
GeForce GTX 780 Ti
GeForce GTX 780
GeForce GTX 770
GeForce GTX 760 Ti
GeForce GTX 760
GeForce GTX 690
GeForce GTX 680
GeForce GTX 670
GeForce GTX 660 Ti
GeForce GTX 660
GeForce GTX 650 Ti BOOST
GeForce GTX 480
GeForce GTX 470
GeForce GTX 465
GeForce GTX 460
GeForce GTX 460 SE
GeForce GTS 450
GeForce GTX 555 (OEM)
GeForce GTX 560 Ti (OEM)
GeForce GTX 560
GeForce GTX 550 Ti
GeForce GTX 590
GeForce GTX 660
GeForce GTX 560 Ti
GeForce GTX 545 GDDR5
GeForce GTX DDR3
GeForce GTX 570
GeForce 9800 GT
GeForce GTX 580
GeForce 9600 GT
GeForce 8500 GT
GeForce 8600 GTS
GeForce 8600 GT
GeForce 8400 GS
GeForce GTX 275X
GeForce GTS 150
GeForce GT 130
GeForce GT 120
GeForce GTS 250
GeForce GTX 285
GeForce GTX 295
GeForce GTX 295
GeForce 8800 ULTRA
GeForce GTX 280
GeForce 8800 GTX
GeForce 9800 GX2
GeForce GTX 260
GeForce 9400 GT
GeForce 9500 GT
GeForce 9800 GTX
GeForce 9800 GTX+

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Aleksandar Cosic

Alex is a Computer Science student and a former game designer. That has enabled him to develop skills in critical thinking and fair analysis. As a CS student, Aleksandar has very in-depth technical knowledge about computers, and he also likes to stay current with new technologies.