The Dell Precision M4400 Mobile Workstation Supports Single and Dual Drive Configurations. (One 2.5" Solid State Drive or Hard Drive in the Internal Primary Bay and One 2.5" Solid State Drive or Hard Drive in the Dell Removable Modular Bay Carrier) Note: The second 2.5" Drive is optional and is located in the optical drive bay when installed. If replacing the optical drive for a second 2.5" Drive, you will need the Dell modular bay drive carrier for installation.