The Lenovo ThinkPad P51s Laptop Comes in 2 Different Drive Options from Lenovo and Supports Single and Dual Drive Configurations. (One M.2 NGFF (2280) Solid State Drive in a Adapter Bracket and/or One M.2 NGFF (2242) Solid State Drive in the WWAN Slot) or (One 2.5" Solid State Drive or Hard Drive and/or One M.2 NGFF (2242) Solid State Drive in the WWAN Slot) Note: When the M.2 (2280) Drive is installed, the M.2 Drive occupies the 2.5" Drive bay using a adapter bracket that is installed in the 2.5" Drive caddy. If replacing the 2.5" Drive for a M.2 Drive, you will need the M.2 adapter bracket caddy p/n 01AY476 and the PCIe SSD cable p/n 01ER035 for installation. If replacing the M.2 Drive for a 2.5" Drive, you will need the 2.5" Drive caddy (remove from M.2 SSD adapter bracket) and the HDD SATA cable p/n 01ER034 for installation. The M.2 (2280) Drive is PCIe NVMe 3.0 x4 but runs at PCIe NVMe 3.0 x2 speeds due to the M.2 adapter bracket limitations.