SLI/Crossfire: What Is It, Do I Need It?
You may have heard of the term SLI, or the term Crossfire; but you might not have known what it meant.
When Do You Need SLI/Crossfire?
When shopping for a video card, you should always get the single best card you can afford, unless you are planning on running at resolution that requires SLI to play games at the desired quality (which is generally 4K at high/max quality).
This is an older version of my own computer, using a pair of GTX 970s in SLI.
I started with a single GTX 760 2GB, added another GTX 760 2GB later on for SLI GTX 760 2GB.
I then traded the SLI GTX 760 2GB for a single GTX 970 4GB.
Later on, I added another GTX 970 4GB for SLI GTX 970 4GB. This is what you see in the picture.
What Is SLI Technology?
SLI is a technology developed by the GPU manufacturer Nvidia. To get technical...Scalable Link Interface (SLI) is a brand name for a multi-GPU technology developed by NVIDIA for linking two or more video cards together to produce a single output.
SLI is an algorithm of parallel processing for computer graphics, meant to increase the processing power available for graphics. Basically, SLI allows you to connect several (up to 4) matching GPUs together to act as one.
SLI setups include 2-way, 3-way, 4-way, and Quad. I’ll explain the difference between 4-way and Quad shortly.
SLI Performance Gains
SLI generally results in a 60-90% increase in framerate (though this is typically only while running a 2-way setup).
This is due to scaling, which does best in two-GPU setups (not necessarily two-card setups).
3 and 4-way SLI
Adding more GPUs allows you to get more performance, but the gains diminish rapidly.
In addition, having more than 1 GPU will almost always require you to have a high-end CPU (at least a normal quad-core i7), and 4-way/Quad SLI will require a very high-end CPU (hex or eight-core i7, or a Xeon).
This is because when you add more GPU, you want that additional GPU to run freely, and not slow down.
This means having a powerful CPU to keep feeding the GPU information, as a lack of information will result in lag, stuttering, poor quality, and potentially crashing.
What CPU for SLI?
If you’re using a simple 2-way SLI setup, a normal unlocked quad-core i7 will do fine (the x700K variants). Be sure you have enough power for the additional card, and proper airflow/cooling.
It’s also recommended to have proper cooling for the CPU, as there will be a substantial load on the CPU while running SLI.
4-Way vs Quad SLI
Back to 4-way vs Quad SLI. 4-way SLI means running 4 individual GPUs together, while Quad-SLI means running 2 dual-GPU cards together.
As you might think, Quad-SLI scales better, as there are less cards to manage.
More cards means more work to be done, and more room for error. 4-way SLI also adds a tremendous amount of heat, and poor scaling, as well as massive power draw.
Nvidia also does not support more than 2-way SLI with the Pascal-series GPUs (the older cards did support 3 and 4-way/Quad SLI). You can still run 4 Pascal GPUs, but you’ll be restricted to getting full use only in synthetic benchmarks, not games.
You also won’t be able to use the High-Bandwidth (HB) SLI bridge that Nvidia developed specifically for the Pascal architecture.
Crossfire is much of the same technology as SLI, and was developed by AMD.