The HP ZBook Studio G4 Mobile Workstation Supports Either Single or Dual Drive Configurations Depending on the Size Battery Installed. (Two M.2 NGFF (2280) Solid State Drives with the Smaller 4-cell 64WHr Battery Installed) or (One M.2 NGFF (2280) Solid State Drive with the Larger 8-cell 92Whr Battery Installed) Note: Models that have the larger 8-cell 92WHr battery installed do not support the second M.2 Drive due to the larger battery occupying the M.2 Drive bay. If installing the second M.2 (2280) Drive with the smaller 4-cell 64WHr battery, you will need the M.2 SSD bracket standoff p/n 840966-001 for installation. (Both M.2 slots support SATA and PCIe NVMe Solid State Drives)