A:Answer I believe they are all Pcie x4 slots. The included SSD runs in SATA mode. You can replace it with an M.2 Pcie SSD which will run much faster. There is also an additional 2280 size M.2 slot and a half height slot. Not sure what one can do with the smaller slot. I added a Pcie SSD to the second slot and cloned the stock SSD to it so it's now my OS drive. I kept the original SSD for my User files (documents, pictures, videos, music, downloads)