The Dell Precision 15 3000 (3520) Mobile Workstation Comes in 3 Different Drive Options Depending on the Battery Installed and Supports Single Drive Configuration Only. (One 2.5" Solid State Drive or Hard Drive or One M.2 NGFF (2280) Solid State Drive with the Smaller 4-cell 68Whr Battery Installed) or (One M.2 NGFF (2280) Solid State Drive with the Larger 6-cell 92Whr Battery Installed) Note: Models that have the larger 92Whr battery installed do not support 2.5" Drives due to the larger battery occupying the 2.5" Drive bay. When the M.2 (2280) Drive is installed with the smaller 68Whr battery, the M.2 Drive occupies the 2.5" Drive bay. If replacing the 2.5" Drive for a M.2 Drive, you will need the M.2 thermal support bracket p/n X3DN4 and mounting bracket p/n 2FFR0 for installation. If replacing the M.2 Drive for a 2.5" Drive, you will need the 2.5" Drive caddy p/n 6F7DD and cable p/n 6NVFT for installation. (The M.2 slot supports SATA and PCIe NVMe Solid State Drives)