A GPS navigation unit that is built into the dashboard or that replaces the factory head unit in a car. It offers navigation along with a raft of audio/video functions such as CD/DVD, MP3, iPod, hands-free cellphone via Bluetooth and satellite radio. The navigation maps are loaded via DVD or hard disk, and hard disk systems can typically rip a CD to an MP3 library while playing the songs.In the mid-1990s, car navigation systems emerged, and by 2000, in-dash systems became a luxury car option. Subsequently, after-market in-dash navs became available, and factory installed units soon migrated to lower priced cars.Where To?Not only can the system direct you to a specific street address, but it can guide you to the nearest gas station, hotel, restaurant or other point of interest (POI). Top-end units can hold 10 million or more POIs.Voice Out and InNavigation systems all offer voice output for turn-by-turn directions. While older units verbalize only the distance to the next turn, newer units pronounce the street names.Some navs include voice recognition for setting the route and controlling the unit. Voice commands allow the driver to concentrate on the road, while working the navigation and audio/video functions.Speed Pulse ConnectionOne advantage of many in-dash units over portable navigation systems is that they monitor the speed of the automobile. Combined with a gyroscope, the unit can track the vehicle while it is in a tunnel, in the lower level of a two-level bridge or in a city or other location where line of sight to three satellites is not possible.The speed is monitored by wiring the unit to the automobile's speed pulse signal, which can be a discrete wire or encoded frames in a digital bus. If the speed pulse is in the bus, adapters can tap the bus and extract the signal (see CAN bus). Most high-end, in-dash units use speed pulse, but some do not, relying solely on the GPS and auxiliary correction, such as WAAS, to pinpoint their location. See portable GPS, GPS and WAAS.