The HP ZBook 17 Mobile Workstation Supports up to 4 Drives. (Two 2.5" Drives and/or One mSATA 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 primary or secondary 2.5" Drive was not installed from HP, you will need the 2.5" Drive bracket p/n 734280-001 for installation.