SLI, or Scalable Link Interface, is the technology to connect two GPUs to have more graphics processing and nearly double the performance. This is specifically for NVIDIA-based cards. When this process is done with AMD cards, it is called Crossfire – though SLI is an umbrella term.
As you build your custom gaming rig, you may question if you can use two different graphics cards in your SLI setup. Perhaps you could only find one of one kind of card but were able to find another similar card. Maybe you already have a decent card in your old build, bought an upgrade, and are considering chaining the two together.
Already, the answer looks like it requires that you have two NVIDIA cards or two AMD cards.
Unfortunately, you cannot SLI two different NVIDIA GPUs because NVIDIA does not allow this for their cards.
It’s time to get more in-depth about the matter.
While you need to use two (or three, or four) GTX 1070s or multiple RTX 2080s to SLI the cards together, the cards do not have to be from the same brand, and they only need to have the same chipset.
Thus, an ASUS RTX 2080 Ti can be used with an MSI 2080 Ti, and the point is that they are both 2080 Ti. And yes, 2080 is different from 2080 Ti, which is different from 2080 Super.
The chipset must be the same, though the manufacturer does not matter.
You may then ask if the VRAM amount matters. Technically, it does. If you have two cards with identical chipsets but not identical VRAM, the SLI will still work, but the capabilities will automatically operate at the lower of the two capacities.
So if you have a 6 GB card and a 9 GB card, it will operate at 6 GB, not 9 GB or 7.5 GB (halfway between the two.)
Other Things To Consider
Here are the other things that you need to look at.
Your motherboard needs to have enough PCIe slots that will run at a minimum of x8 lanes, but preferably x16 lanes with multiple GPUs installed. Additionally, the motherboard needs to support SLI because otherwise, it will automatically throttle your cards to x4, and you gain nothing from SLI.
Don’t worry about chaining three or four cards together, though. That was a thing of the past; cards these days are so much more powerful that the capability is generally only reserved for massive 3D builds.
Ideally, it would help if you got a strong gaming CPU to prevent your GPUs from being bottlenecked.
Your power supply needs to have more than enough wattage to cover the load of multiple GPUs and have enough power connector slots.
GPUs generate a lot of heat, which means they need to be kept cool. Otherwise, they will start to slow down or fail. You need to have enough airflow in the case, plenty of fans, and an excellent water-cooling set up for your CPU, if not water blocks for your GPUs as well.
For a while, especially with DirectX 12, SLI seemed to be dying out entirely. However, with the new generation of cards coming out, SLI is becoming more popular again. Whether or not your games will benefit from SLI has to do more with drivers than individual games.
There is a lot of patience required with SLI in general, and this is one of those areas where you will have to check each game for SLI optimization manually and, in some cases, accept that there is no SLI compatibility.
The AMD answer to SLI is Crossfire, and it works on a similar principle. For the most part, everything works the same, though Crossfire allows you to chain two similar but not identical chipsets together, like a Radeon 7950 with a Radeon 7970. They are close enough to be bridged but are not precisely the same.
So, when considering SLI for your gaming build, you need to have multiple cards with identical chipsets, though they do not have to have the same manufacturer or VRAM. Ideally, they would be from the same manufacturer and have the same VRAM. This will ensure there are no performance discrepancies and that they would be more aesthetically pleasing.