The Samsung 960 PRO 512 GiB is a high-end SSD that uses M.2 form factor, PCI Express 3.0 x4 connection, and NVMe standard. It is found on 512 GiB, 1 TiB and 2 TiB capacities, and its annouced maximum read speed is 3,500 MiB/s and write speed of 2,100 MiB/s.
While the most popular SSDs use the 2.5 inches form factor (which is the same size of a standard laptop HDD), the M.2 form factor is being more and more common. The main reason is that this standard allows both the SATA-600 and the PCI Express x4 connections, that has a higher maximum bandwidth. One of the models that use this standard is the Kingston HyperX Predator. There are also SSDs that uses the PCI Express 3.0 x4 connection, but come as an expansion card, like the Intel SSD 750 Series.