The Dell Precision M6800 Mobile Workstation Supports up to 4 Drives. (One 2.5" Solid State Drive or Hard Drive in the Easy Eject Drive Bay and/or One 2.5" Solid State Drive or Hard Drive in the Internal Drive Bay and/or One mSATA Solid State Drive + One 2.5" Solid State Drive or Hard Drive in the Removable 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 modular bay drive carrier p/n MRR89 for installation. If installing a 2.5" Drive in the easy eject drive bay, you will need the 2.5" Drive easy eject drive bay caddy p/n 794WN for installation. If installing the secondary 2.5" Drive in the internal drive bay, you will need the 2.5" Drive internal secondary drive bay caddy p/n CGYW1 for installation.