Scalable Link Interface is a mechanism that allows the performance of two or more graphics cards plugged into PCI Express slots to be combined. It was created by graphics card manufacturer NVIDIA to work with NVIDIA graphics cards only. CrossFire is a similar technology launched by ATI (later taken over by AMD) that works only with their graphics cards. For SIl I CrossFire to work, the graphics cards must be of the same type, and the motherboard should support the technology, besides having two PClli X16 slots.

The graphics cards are connected via a special cable called a Bridge Connector (though CrossFire models connect through the PClli bus or one of the cards should be a CrossFire edition card). In SIl mode, one of the cards acts as a master, and the output is available only through it. The graphics load is distributed in two ways. In Split Frame Rendering, the display area is divided into two halves horizontally, with each card responsible for one half; in Alternate Frame Rendering, each card renders every alternate frame.