A very common question I get from gamers that build their gaming rig with two different brands of GPUs is if they can SLI them.
Well, the answer is no. NVIDIA SLI only works only between the same model NVIDIA GPUs. On the other hand, AMD CrossFire works between different AMD GPU models.
Some of you are going to ask what SLI and Crossfire are, so let’s start with that first.
What are SLI AND CROSSFIRE?
SLI is Nvidia’s multi-GPU solution that allows you to use two or more GPUs at once.
It works by splitting the rendering work between multiple video cards to maximize performance.
SLI technology supports linking two identical NVIDIA graphics cards together to produce a single output.
On the other hand, Crossfire is AMD’s own multi-GPU solution that works similarly to Nvidia’s SLI.
The difference is that instead of linking two identical graphics cards, it works by linking any two AMD GPUs as long as they are from the same series.
Can I use 2 different Nvidia GPUs?
As we already said, NVIDIA SLI only works between the same model NVIDIA graphics cards.
The models should be exactly the same for example, GTX 980 Ti won’t be supported with GTX 980.
Should the GPUs be the same brand?
No, the brand doesn’t matter. As long as the GPUs are identical, you can use the Scalable Link Interface.
What matters is the chipset; as long as the GPUs are the same, you will be able to use SLI.
How about the VRAM?
Using two GPUs with different amounts of VRAM is okay, but the performance will be limited according to the one with less RAM.
For example, if you use a GTX 980 2GB with a GTX 980 4GB, the GTX 980 the performance will be limited down to 2GB VRAM each.
Related Article: Can You Use An Nvidia Graphics Card With An AMD Processor?
Requirements to run Scalable Link Interface
Before you get excited and start buying GPUs to build your SLI, there are some requirements that you need to meet for your SLI setup.
- Compatible Motherboard
The first thing to do is make sure your motherboard supports SLI. It doesn’t matter if your motherboard has 2 PCIe x16 slots if they are not SLI compatible.
By reading the manual or checking the manufacturer’s website, you can easily see if your motherboard is SLI compatible.
It is important to ensure your motherboard supports SLI because if it doesn’t, using more than one GPU can toast it.
- Two or more SLI-compatible GPUs
After you have checked that your motherboard supports SLI, you can now check for compatible GPUs.
As we mentioned above, NVIDIA SLI works between the same GPU, but keep in mind that not all Nvidia GPUs support SLI.
So make sure to buy 2 or more GPUs that support SLI. You can check the list of NVIDIA graphics cards that support SLI in their website.
- Two or more PCIe x16 slots
If your motherboard is SLI compatible, you need to make sure that it has 2 or more PCIe x16 slots. But you should also pay attention to the number of lanes. They should have at least 8 lanes, ideally 16 lanes.
- Your Power Supply Unit
You need to make sure that the PSU is powerful enough to support the GPUs you are planning to use. Also, it needs to have the right number and type of PCI cables that will plug into your GPUs
- A good CPU
You should make sure that you have a good enough CPU to support multiple GPUs. If the CPU is not powerful enough, the GPUs won’t be able to fully unleash their performance leading to bottlenecks.
- Enough RAM Memory
To run multiple GPUs, you need to have enough RAM. It is suggested to have at least 2GB of RAM if you have an x32 bit system and 4GB of RAM if you have an x64 bit system.
How to set up SLI?
In order to set up SLI, you need to understand how it works. The first thing is to learn about the master-slave configuration.
1. Master-Slave Configuration
When you use two or more GPUs, they should be configured to run in a master-slave configuration.
What this means is that one of the GPUs will act as the primary card while the other(s) will act as secondary or helper cards.
The primary GPU (master) takes control of the upper part of the screen, while the secondary (slave) takes control of the bottom part. When it is finished rendering, the slave sends what is done to the master, and then the master takes the final action of displaying everything on your monitor.
You should know about the Master-Slave Configuration because using a card with less memory in the master position will slow down your overall graphics performance.
2. SLI Bridges
Sli Bridges are a must if you want to run two GPUs.
The SLI bridge will connect both cards and transfer the data between them.
It is possible to run SLI without the SLI bridge, but it is not recommended, especially if you have two high-end GPUs.
If you don’t use an SLI bridge, the data transfer will happen through your motherboard’s chipset. This can slow down the data transfer rate and bottleneck the GPUs.
Related Article: What Is GPU Artifacting, And How To Fix It
Are NVLink and Direct 12 killing SLI?
If you thought that SLI was the latest and greatest of NVIDIA’s technologies, think again.
NVIDIA has been working on a new technology called NVLink, which is about 10 times faster than traditional SLI.
NVLink is a super-high-speed protocol developed by NVIDIA that allows data transfer between GPUs. It works just like the SLI Bridge, but it is way faster.
Until a while ago, a game’s compatibility with SLI was dependent on if Nvidia had drivers for that specific game. These drivers were not that efficient, and there were a lot of complaints about performance issues.
I said “until a while ago” because now there’s no need to install Nvidia’s SLI drivers for your GPUs to work.
Now with new tech like Direct 12 & Vulkan graphics API, one can enable SLI without Nvidia’s proprietary drivers.
The game developers are using these new techs to write their own code and use multiple GPUs to their full potential.
The fact that Nvidia stopped developing their own SLI drivers and threw the ball to the game developers along with the NVLink and the new graphics API means one thing, SLI will be a thing of the past soon.
What Can I do if I have a second Nvidia Graphics Card?
I think it is pretty clear now that if you want to use SLI, you should have the same graphic cards.
But what if you have two different Nvidia graphics cards?
This is a pretty common case when someone buys a newer graphics card. For example, when you have a GTX 1060 and want to upgrade to GTX 1070 or 1080.
Now you have an NVidia graphics card that can’t be used for SLI; what can you do with it?
1. Use Nvidia PhysX
What is Nvidia PhysX?
Nvidia PhysX is a technology developed by Nvidia a while ago that allows you to use your GPUs for better physics simulation.
What this means is that instead of using the CPU to calculate how objects interact, the PhysX uses the graphics card to do it. This can result in much more fluid and real-time physics simulation.
That being said, not all games support Nvidia PhysX, so you need to know if your game supports it or not before turning it on.
To set a card to be used for PhysX, you should go to Nvidia Control Panel and do it from there.
But you should be careful because the overall performance will be slower if there is a big difference between your graphics cards.
The only way to know if PhysX will be faster with your setup is to test it.
As I already mentioned, GPU-based PhysX is an older technology, but most modern games still use it.
The only difference is that the PhysX technology is not GPU-based anymore.
Game developers have their own code for calculating physics and use different algorithms. This means that you should test the difference between having PhysX on or off in your game of choice.
Wrapping it up
Before I finish this article, I wanted to clarify that before adding a second graphics card, you should check some things first to either SLI it or use it for the PhysX.
First, do you have a motherboard with a number of lanes that makes sense to add a second graphics card?
For example, if your motherboard has two PCIe x16 slots, and one of them is a “true” x16 with 16 lanes, and the other has only 4 lanes, it will be impossible to gain the full advantage of adding a second GPU.
Related Article: PCIe 2.0 VS 3.0 – What Is The Difference?
Then you should make sure that your PSU can support the additional power draw your second GPU will bring. If your PSU is not strong enough to support a second GPU, it can shut down randomly or deliver insufficient power for your GPUs. This can result in decreased performance, crashes, and damage to the components.
Finally, you should have really good ventilation in your case for adding a second GPU. If you don’t have good ventilation and good airflow, adding more GPUs can cause them to overheat and decrease their lifespan.
Now you know everything there is to know about adding a second GPU to your PC.
You not only know if you can SLI two different GPUs but also if it is possible to use them for the PhysX.
As you can see, there are a lot of things to consider before adding a second GPU and it is not as easy as you may think.
I hope that my article was informative and that now you know more about GPUs than before you started reading this article.
If you have any questions, feel free to ask me in the comments below!
Nick Ryley, is a computer architect and the owner of The Pc Geekz.
His love to play games got him interested in computers in the first place. He wanted to be able to build a gaming PC that could run all the latest games at max settings and this has him pursuing a major in computer architecture!
He started this blog to help people out and answer some of the most common questions about computer building