What is SLI (Scalable Link Interface)?

SLI is the name of the Scalable Link Interface and is a method for connecting only two or more graphics cards and generating only one output signal. In general, SLI is nothing more than ways to connect up to 4 graphics cards, and the system treats them as a single card.

What is SLI (Scalable Link Interface)?

What is SLI in Graphics Card?


The first version of this technology was called Scan-Line Interleave, and it was released in 1998 by 3dfx Interactive, a company that specializes in the production of 3d graphics processors, and then specializes in the design and production of graphics cards that prevailed until the late 1990s, especially between 1997 and 2000.

This technology became evident and famous in Vodoo 2 graphics accelerator chips. Scan-Line Interleave was the first attempt to combine the processing power of two graphics cards, they were connected by a small cable that allowed the sharing of synchronization information.

The feature connector was a technology for VGA and SVGA systems that allowed an expansion card to directly access the video card’s main memory without using the system bus.

Receiving patents, designers, and technologies from 3dfx, Nvidia was responsible for launching the technology under the name of Scalable Connection Interface, and in 2004 changed its work to use it on new computers with a PCI-Express.

How Does It Work?

Using SLI, it is possible to double the computing power of the computer by adding a second identical card to the first one.

You can use two cards from scratch, or you can have a card that supports SLI, and add more when more processing power is required. However, there are times when the procedure is more expensive than buying a new video card.

The Nvidia application requires a motherboard with two PCIe x16 ports. The two cards are connected together by a small printed circuit connector.

The software distributes the load in two ways. The first analyzes the image to be displayed in a frame known as SFR (Split Frame Rendering) and divides the load evenly between the two GPUs.

The second form is called AFR (Alternate Frame Rendering), and each frame is rendered alternately by one GPU, i.e. one frame is processed by the first GPU and the other by the second GPU.

When a box is displayed, the image is sent to the main GPU via the SLI connection and sent to the output. Ideally, this halves processing time, but the actual time is a little longer. NVIDIA says that the performance of the system increased 1.9 times with this configuration.


NVIDIA has implemented two similar systems that can deliver superior improvements in the graphics performance of a system up to 2.8x in 3-Way SLI and 1.6x in the case of Quad-SLI than can be achieved with a simple Graphics card.

One of the most enjoyable options to create a cost-effective SLI system, 3-Way SLI was born with the emergence of the GeForce 8 series and only 8800 GTX and Ultra at that time. Nowadays, it can be used with cards like 9800 GTX of 9 series that can access this technology. These are 3 single-core graphics cards combined with a 6 port connector.

In graphics applications that take advantage of these benefits, as mentioned earlier, you can see up to 2.8x higher performance. However, the energy requirements of this configuration can be a major disadvantage.

For example, 9800 GTX cards require two additional peripheral connectors to provide power consumption that the simple PCI Express socket cannot provide, which can only provide 1000W of 3-Way power supplies.

In response to this problem, NVIDIA launched the Hybrid SLI system, which randomly disables the cards that make up the SLI to save consumption, but this technology is only available for a limited number of motherboards and cards.

Quad-SLI is another implemented SLI option that leaves much to be desired. Although it looks like a simple classic two-card SLI at first glance, it is a combination of two cards. In reality, it turned out to be an explosive combination of 4 cores, because each card requires the use of only one PCI Express combined in it for technology very similar to SLI.

The result is a 4-core SLI system that can be interpreted as a 4-composite single-core card and can actually be evaluated as two “two-in-one”.

The problem is that the very high cost does not justify performance improvements that are only 1.6 times larger, which means that more cores are lower than the total performance multiplication. Also, this improvement can only be seen in a much more limited number of applications than the triple path. For example, Crysis is a video game with high requirements that only show the greatest graphic effects running on this configuration.

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