Nvidia 10 series SLI 3x 4x how does it work?

Question

Video cards

There are two gtx 1080 FE in Sli through the old sli bridge.
Before that I read an article that video cards of the 10th series work only in 2x sli mode. But later I saw a photo that they also work in the quad sli mode. Tell me how the merging process is implemented and if the meaning is in quad sli. And where to buy new bridges sli. And what's the difference with the old bridges. This PC is used for games and multimedia.