NVIDIA GTX 1080/1070 comes with new SLI HB Bridges

With the new GeForce GTX 1080 and GTX 1070 graphics cards, NVIDIA has also introduced a new SLI technology, the SLI HB.

The new SLI HB is available only with the new GP104 GTX 1080 and GTX 1070 graphics cards. The HB stands for High-Bandwidth will double the amount of memory bandwidth available between two cards.
GTX SLI HB Bridges

The new SLI HB uses both SLI fingers and should theoretically double the bandwidth and make SLI much better and faster, which helps to higher display resolutions and better multi-display setups. But the SLI HB only available in rigid bridges so your card placement is limited and the motherboard should have specific PCIe placement.