The Dell Alienware m15 R1 Laptop Supports Either 2 or 3 Drives Depending on the Battery Installed. (One 2.5" Solid State Drive or Hard Drive with the Smaller 4-cell 60Whr Battery Installed and/or Two M.2 NGFF (2280) or (2230) Solid State Drives) or (Two M.2 NGFF (2280) or (2230) Solid State Drives with the Larger 6-cell 90Whr Battery Installed) Note: Machines that have the larger 90Whr battery installed do not support 2.5" Drives due to the larger battery occupying the 2.5" Drive bay. The M.2 (2230) Drive uses a adapter bracket to accommodate for the larger M.2 (2280) Slot. If installing a 2.5" Drive in machines with the smaller 60Whr battery installed, you will need the 2.5" Drive caddy p/n 68WXJ and Drive cable p/n PCYYV for installation. (M.2 slot 1 SSD#1 supports SATA and PCIe NVMe Drives and M.2 slot 2 SSD#2 supports PCIe NVMe Drives only)