The Dell Precision M2800 Mobile Workstation Comes in 2 Different Drive Options from Dell and Supports Single and Dual Drive Configurations. (One 2.5" Solid State Drive or Hard Drive and One 2.5" Solid State Drive or Hard Drive in the Dell Modular Bay) or (One mSATA Solid State Drive in a Adapter Caddy and One 2.5" Solid State Drive or Hard Drive in the Dell Modular Bay) Note: When the mSATA Drive is installed, the mSATA Drive occupies the 2.5" Drive bay using a adapter caddy. 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. If replacing the mSATA Drive for a 2.5" Drive, you will need the 2.5" Drive caddy p/n 73YH2 and 7mm rubber rails p/n 5D56T/N80MN for installation. If replacing the 2.5" Drive for a mSATA Drive, you will need the mSATA adapter caddy p/n 86MKK for installation.