SLI is the Nvidia brand name for connecting 2 or more Nvidia Graphics cards together for improved rendering.
Appearing in 1998 the technology was first used by company 3dfx on their Voodoo2 graphics card line, but later bought by Nvidia and the technology was put on the back burner for a while. In 2004, Nvidia released SLI with updates to allow it to work with PCIe buses.
Nvidia graphics cards will work together in SLI in three main modes: SLI anti-aliasing, SFR, and AFR. You can select and change these modes in the Nvidia Control Panel, which should have been installed onto your computer when you installed your video card drivers.
Split Frame Rendering (SFR)
This method takes the frame that needs to be rendered, analyzes it, and then splits up the frame horizontally into as many pieces as there are cards, and sends the workload between them. It can split the frame how it sees fit based on what’s in the frame.
For example, if the frame contains a mostly empty, static sky in the top half of the frame (less resource intensive), but moving characters in the bottom half (more intensive), then it will determine that one card would be doing more work if it is merely split 50/50. So, the card responsible for the upper portion of the screen may receive about 60% of the screen real estate while the card responsible for the bottom will only have to process the bottom 40%. (Note: these percentages are just vague examples, not concrete numbers.)
Alternate Frame Rendering (AFR)
In this mode, the frames are queued up and each card renders a full frame. So, if you are running 2 cards, then one would be responsible for even numbered frames while the other would be responsible for odd numbered frames. This is often considered more effective than SFR for achieving higher frame rates, but it can also cause issues such as micro stuttering.
Keyword: Micro Stuttering – This it when you see visual stutters on your screen caused by a discrepancy in frame rendering times between cards. If the cards are not synced up properly, or they don’t have enough information to guess the next frame that needs to be rendered, then you will see a delay.
This mode allows for a better image quality, as opposed to pushing higher frame rates. It works to split the anti-aliasing workload between the cards, increasing the overall quality of your image.
Using this mode can unlock higher anti-aliasing modes within games (such as SLI 8x, 16x, and even 32x on quad-SLI systems).
Compatibility and Issues
Alright, so all you need to do is buy two graphics cards? Do I just slap any two Nvidia cards into my motherboard and call it a day? Unfortunately, it’s not that simple. But then again, it never is…
Two (or more) of a Kind
The first thing you need to know is what graphics cards will pair together; not just any two cards will work. They have to be the same GPU, and they have to have the same amount of video RAM.
For example, if you had a GTX 1070 TI 8GB made by Asus, and another of the exact same specs, but made by MSI, it would still work. A GTX 1070 and a GTX 1080 are not compatible, as they are not the same GPU.
You will also need to make sure that the graphics cards are SLI compatible themselves, as cards without the SLI port on top may not be compatible. Also, it is worth noting that Nvidia killed support for 3 and 4 card SLI for the GTX 10 series.
Slots and Plugs
Next on the list is your motherboard and power supply. These will both need to be SLI compatible.
This means that your motherboard will need enough PCIe x16 slots to match your number of GPUs and your power supply will need enough PCIe connectors to power the amount of cards you will be using.
A common misconception about SLI is that you can get double, triple, or even quadruple video RAM with more graphics cards. Unfortunately, Nvidia SLI only uses the RAM from one card, as each card needs to access the same information at the same time.
What is the SLI Bridge?
So whats a sli bridge? The last thing you will need in order to run your SLI setup is an SLI bridge enabling multi GPU technology in a master slave configuration. Nvidia uses a physical connector to bridge the graphics cards together, allowing them to communicate with each other without using precious bandwidth on the PCIe slots.
You will need one of two SLI bridges: either the standard bridge (for less powerful cards), or a high-bandwidth bridge (for the more powerful cards).
SLI Bridge Series
Pixel Clock Speed
Recommended Monitor Support
1920×1080 through 2560×1440 @60 Hz
Up to 5k and surround sound
If you have more powerful cards (like say the GTX 1080), you can use a standard bridge, but it won’t allow for the full performance of the cards. The high-bandwidth brides would allow for this.
So we know what SLI is, how it works, and what you need to use it. But should you rush off to buy that second and third GTX 1080 TI, and have to tell your wife that the whole baby will have to wait?
Well, that’s where the waters get a bit murky. While Nvidia claims that twice the performance is possible with twice the cards, that’s rarely ever the case.
The problem is, games don’t natively know how to properly use multiple video cards, and SLI profiles have to be added into them by the developers. This is not an easy task, and can be very time consuming, so most developers don’t take the time.
This means that unless you’re playing a AAA game, it’s possible that there will be no performance increase (in fact, there’s even the possibility of a decrease in performance).
Performance for each game will vary, though. So that doesn’t mean it will be completely useless for you, just that you should be aware of this before investing in the technology or any specific games. You can see a list of SLI certified games here, just in case.
But don’t let us be the final voice on the matter. Is SLI a viable proposition for you, or are you going to just save up for a completely new graphics card?
SLI configuration won’t run on operating systems that do not support SLI. Operating systems that fully support SLI are given below:
Windows Vista 32-bit
Windows Vista 64-bit
Windows 7 32-bit
Windows 7 64-bit
Windows 8 32-bit
Windows 8 64-bit
Windows 10 32-bit
Windows 10 64-bit
Also you require 2GB to 4GB RAM (for 64-bit OS) for SLI.
As of now you do not have to download special drivers for SLI because NVIDIA ForceWare Unified Driver Architecture (UDA) supports SLI technology. You just have to download the latest driver for your graphics card as all the SLI profiles and SLI drivers comes include in it.
Powerful Power Supply
You need a very powerful and reliable power supply if you are running two or more high-end graphics cards in SLI mode on your computer. This is because each high-end graphics cards can consume up to 200 – 250 Watts of power which results in tremendous power requirements altogether.
SLI Games & Applications
All games and applications do not support SLI technology. You can only see performance increase in games and applications that are GPU bound and supports multi-GPU configuration. In turn, Nvidia includes SLI profiles in their driver package so that you don’t have to configure anything. Almost all the latest games support SLI and you can really increase your gaming performance to much greater level.
Types of SLI Configuration
There are three types of SLI configurations in which you can connect multiple GPUs (up to 4).
2-Way SLI – In this, you can connect two single GPU graphics cards in SLI mode using 2-way SLI Bridge.
3-Way SLI – In this, you can three single GPU graphics cards in SLI using 3-way SLI Bridge.
4-Way SLI or Quad SLI – This is also called Quad SLI and in this, you can connect 4 single GPUGraphics Cards in SLI using 4-way SLI Bridge or can connect two dual GPU graphics cards using 2-way SLI bridge. You cannot connect 3 or 4 dual GPU graphics cards in SLI because that would make it Hexa and Octa SLI configuration which does not exist.
Note: 2-way SLI is the most popular and active SLI configuration used today because Nvidia has reportedly dropped most of the support for 3-way and 4-way SLI. This is because of the complexity involved in driver development. Modern graphics cards such as GTX 1070, GTX 1080 and higher will only support 2-way SLI.
There are various types of SLI modes of operation which are being mentioned below:
Split Frame Rendering (SFR) – In this mode GPUs split the workload equally to render the image on the screen.
Alternate Frame Rendering (AFR) – In this mode one GPU renders odd frames and other GPU renders even frames alternatively.
SLI Antialiasing – In this mode two GPUs split the workload of Antialiasing to provide smoother and superior image quality without any jagged edges.
Hybrid SLI – In Hybrid SLI, discrete GPU (Graphics Card) and IGP (Integrated Graphics) work together to increase performance. It can be found on laptops too.
Important Note – You need a powerful CPU for high-end SLI configuration otherwise the CPU will be a bottleneck for the graphics cards and performance will suffer drastically.
List of Desktop Graphics Cards supporting SLI
Here is the list of all SLI supported desktop graphics cards from Nvidia.