The HP ProBook 645 G1 Notebook Supports Single and Dual Drive Configurations. (One 2.5" Solid State Drive or Hard Drive and/or One M.2 NGFF (2242) 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 738395-001 (Includes: 2.5" Drive bracket, connector and screws) for installation. (The M.2 slot support SATA only Solid State Drives)