The Dell Latitude-3420 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 41Whr 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 54Whr Battery Installed) Note: Models that have the larger 4-cell 54Whr 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 conversion bracket to accommodate the form factor. If the 2.5" Drive was not installed from Dell on models with the smaller 3-cell 41Whr battery, you will need the 2.5" Drive caddy p/n 061CCY and cable p/n 0K8TGP for installation. (The M.2 slot supports PCIe NVMe Solid State Drives)