The Dreamcast controller features a similar design to the Sega Saturn's analog controller, offering an analog stick, a D-pad, a Start button, four action buttons (labeled A, B, X, and Y, two buttons less than the Saturn), and two analog triggers on the underside. It also contains two slots which can hold memory cards, rumble packs, VMUs, or microphones, with a window on the front of the controller through which the VMU's display can be seen. In contrast to most previous game controllers, the controller cord comes out from the bottom of the controller. There is a divot in the back of the VMU slots which the cord can be snapped into, making it more traditional.
Source: Wikipedia, "Dreamcast accessories", available under the CC-BY-SA License.