The Lenovo ThinkPad P51 Laptop Supports up to 3 Drives. (One 2.5" Solid State Drive or Hard Drive and/or Two M.2 NGFF (2280) Solid State Drives) Note: The M.2 Drives use a SSD NVMe adapter bracket tray p/n 00UR868 for installation. If the 2.5" Drive was not installed from Lenovo, you will need the 2.5" Drive storage kit p/n 4XB0L63274 for installation. (Both M.2 slots support PCIe NVMe Solid State Drives)