The Dell Precision 15 3000 (3550) Mobile Workstation Comes in 2 Different Drive Options Depending on the Battery Installed and Supports Single Drive Configuration Only. (One 2.5" Solid State Drive or Hard Drive with the Smaller 3-cell 42Whr/51Whr Battery Installed) 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 68Whr battery installed do not support 2.5" Drives due to the larger battery occupying the 2.5" Drive bay. When the M.2 (2280) or (2230) Drive is installed with the smaller 42Whr/51Whr battery, the M.2 Drive occupies the 2.5" Drive bay. The M.2 (2230) Drive uses a adapter bracket p/n 07HMH to accommodate for the larger M.2 (2280) slot. If replacing the 2.5" Drive for a M.2 Drive, you will need the M.2 Drive thermal plate p/n 85J62 and support bracket p/n KJK50 for installation. If replacing the M.2 Drive for a 2.5" Drive, you will need the 2.5" Drive caddy p/n ND8N9 and cable p/n XY5F7 for installation. (The M.2 slot supports PCIe NVMe Solid State Drives)