The HP ZBook 15 G2 Mobile Workstation Supports up to 3 Drives. (One 2.5" Solid State Drive or Hard Drive and/or One M.2 NGFF (2260) Solid State Drive and One 2.5" Drive in the Upgrade Bay) Note: If installing a 2.5" Drive in replace of the optical drive, you will need the upgrade bay tray p/n 734298-001 for installation. If the 2.5" Drive was not Installed from HP, you will need the 2.5" Drive bracket p/n 734280-001 for installation.