The HP ZBook 15 G4 Mobile Workstation Supports up to 3 Drives. (One 2.5" Solid State Drive or Hard Drive and/or Two M.2 NGFF (2280) Solid State Drives) Note: If the 2.5" Drive was not installed from HP, you will need the 2.5" Drive hardware kit p/n 848231-001 (Includes: 2.5" Drive bracket and cable) for installation. (Both M.2 slots support SATA and PCIe NVMe Solid State Drives)