This Machine Supports 2 Different Drive Options and Supports Single Drive Configuration Only. (One 2.5" Solid State Drive or Hard Drive) or (One M.2 NGFF (2280) Solid State Drive using a M.2 Drive Holder) Note: When the M.2 (2280) Drive is installed, the M.2 Drive occupies the 2.5" Drive bay using a M.2 Drive mounting holder. If replacing the M.2 Drive for a 2.5" Drive, you will need the 2.5" Drive mounting rails p/n 856377-001 and cable p/n 856352-001 for installation. If replacing the 2.5" Drive for a M.2 Drive, you will need the M.2 Drive mounting holder p/n 856385-001 and drive board p/n 856210-001 and cable p/n 856353-001 for installation. (The M.2 Drive board supports SATA only Solid State Drives)