The Dell Latitude 3400 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 42Whr 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 56Whr Battery Installed) Note: Models that have the larger 4-cell 56Whr battery installed do not support 2.5" Drives due to the larger battery occupying the 2.5" Drive bay. The M.2 slot supports M.2 (2280) and (2230) Drives by moving the metal mounting bracket to accommodate the form factor. If the 2.5" Drive was not installed from Dell on models with the smaller 3-cell 42Whr battery installed, you will need the 2.5" Drive caddy p/n 4174N and cable p/n 7N2N2 for installation. (The M.2 slot supports SATA and PCIe NVMe Solid State Drives)