The Dell Inspiron 15 7000 (7591) 2-in-1 Laptop Supports Either 1 or 2 Drives Depending on the Battery Installed. (One 2.5" Solid State Drive or Hard Drive with the Smaller 3-cell 51Whr Battery Installed and/or One M.2 NGFF (2280) or (2230) Solid State Drive) or (One M.2 NGFF (2280) or (2230) Solid State Drive with the Larger 4-cell 68Whr Battery Installed) Note: Models that have the larger 4-cell 68Whr battery installed do not support 2.5" Drives due to the larger battery occupying the 2.5" Drive bay. If the 2.5" Drive was not installed from Dell on models with the smaller 51Whr battery, you will need the 2.5" Drive caddy and cable for installation. The M.2 slot supports M.2 (2280) and (2230) Drives by moving the metal mounting bracket to accommodate the form factor. (The M.2 slot supports PCIe NVMe Solid State Drives)