The HP ZBook 15u G4 Mobile Workstation Supports Single and Dual Drive Configurations. (One 2.5" Solid State Drive or Hard Drive and/or One M.2 NGFF (2280) Solid State Drive) Note: If the 2.5" Drive was not installed from HP, you will need the 2.5" Drive hardware kit p/n 821665-001 (Includes: 2.5" Drive bracket and screws) for installation. (The M.2 slot supports SATA and PCIe NVMe Solid State Drives)