The Dell Precision M6700 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 and 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 a third 2.5" Drive, you will need the Dell modular bay drive carrier 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.