It is a separate piece of hardware. The standard HDS-10 unit comes with a transducer the plugs into to back of the unit. When you add Structure Scan it comes with an additional transducer mounted beside the first and a separate box to plug both transducers in to. It then connects to your HDS unit. When you start interfacing satellite weather, radar and other peripherals you need an ethernet hub similar to the Structure Scan box to connect everything to. Go to the Lowrance site and you will see the connection configurations.