The Dell Precision M6500 Mobile Workstation Supports up to 4 Drives. (Two 2.5" Solid State Drive or Hard Drives in the Internal Bays and/or One mSATA Solid State Drive and One 2.5" Solid State Drive or Hard Drive in the E-Modular Drive Bay Carrier) Note: The third 2.5" Drive is optional and is located in the optical drive bay when installed. If replacing the optical drive for the third 2.5" Drive, you will need the Dell E-Modular Bay Drive Carrier for installation. If installing the primary 2.5" Drive, you will need the 2.5" Drive (HDD1) primary drive caddy p/n N361F for installation. If installing the secondary 2.5" Drive, you will need the 2.5" Drive (HDD2) secondary drive caddy p/n 23XM2 and interposer connector p/n FP2P7 for installation.