The HP ProBook 645 G3 Notebook Comes in 2 Different Drive Options from HP and Supports Single Drive Configuration Only. (One 2.5" Solid State Drive or Hard Drive) or (One M.2 NGFF (2280) Solid State Drive) Note: When the M.2 (2280) Drive is installed, the M.2 Drive occupies the 2.5" Drive bay. If replacing the M.2 Drive for a 2.5" Drive, you will need the 2.5" Drive caddy p/n 917460-001 for installation. (The M.2 slot supports SATA and PCIe NVMe Solid State Drives)