The Dell Precision 7720 Mobile Workstation Comes in 2 Different Drive Options from Dell and Supports up to 3 Drives. (One 2.5" Solid State Drive or Hard Drive and/or Two M.2 NGFF (2280) Solid State Drives) or (Three M.2 NGFF (2280) Solid State Drives) Note: When the third M.2 Drive is installed, the M.2 Drive occupies the 2.5" Drive bay using a adapter bracket with a M.2 interposer board. If replacing the 2.5" Drive for a third M.2 Drive, you will need the 2.5" Drive caddy p/n KN40P (remove this from the 2.5" Drive) and the M.2 bracket p/n Y1WJX (installs in the KN40P caddy) and the M.2 interposer board p/n WPTND (installs in the Y1WJX M.2 bracket) and the M.2 thermal cover p/n HR8P8 for installation. If installing a 2.5" Drive in the empty drive bay, you will need the 2.5" Drive caddy p/n KN40P for installation. If installing a M.2 (2280) Drive in either of the two empty M.2 slots, you will need the M.2 Drive thermal cooling bracket p/n HR8P8 for installation. (The M.2 slots support PCIe NVMe Solid State Drives)