The Lenovo ThinkPad T520 Laptop Supports up to 3 Drives. (One 2.5" Solid State Drive or Hard Drive in the Primary Drive Bay and/or One mSATA Solid State Drive and One 2.5" Solid State Drive or Hard Drive in the Optical Bay) Note: The second 2.5" Drive replaces the optical drive when installed. If installing the second 2.5" Drive in replace of the optical drive, you will need the 2nd HDD ultrabay slim tray for installation.