The Asus ZenBook Pro UX501VW Laptop Supports Single or Dual Drive Configurations Depending on the Battery Installed. (Options with the Smaller 4-cell 60Whr Battery Installed: One 2.5" Solid State Drive or Hard Drive and/or One M.2 NGFF (2280) Solid State Drive) or (Option with the Larger 6-cell 96Whr Battery Installed: One M.2 NGFF (2280) Solid State Drive) Note: Models that have the larger 6-cell 96Whr battery installed do not support a 2.5" Drive due to the larger battery occupying the 2.5" Drive bay. If the 2.5" Drive was not installed from Asus in models with the smaller 4-cell 60Whr battery installed, you will need the 2.5" Drive caddy p/n 13NB07D1M05011 and connector board p/n 90NB0870-R10030 for installation. (The M.2 slot supports SATA and PCIe NVMe Solid State Drives)