The control center and user interface for an automobile's entertainment center, which typically resides in the center of the dashboard. It provides the main controls for the radios (any combination of AM, FM, XM, Sirius, HD Radio) as well as a CD/DVD player, GPS navigation, Bluetooth cellphone integration, hard disk storage for music and iPod connector. There may be auxiliary controls on the steering wheel. Self-Contained The head units have their own amplifiers for powering the speakers, but may have optional outputs for more powerful, stand-alone amplifiers. After market products typically have the most flexibility, although head units in luxury cars have very elaborate audio systems. See in-dash navigation.