Most fit into the palm of your hand, and have a thick but short antenna. They all have some sort of display screen, which come in various resolutions and are usually backlit. Some units have an internal memory from which you can access a Map Database, displaying major roads and highways, cities and other navigable details. More advanced units will even allow you to load onto your device more comprehensive street detail, via an additional Flash memory. Many GPS navigators will also provide you with additional information like distance, bearing, speed, time to go, elevations and more.
All units work on a rechargeable battery.
To pinpoint your position on the earth, and your distance from your desired destination, all GPS units use some type of channel tracking system. The more satellites needed or used to track your location, the more accurate the reading. Average handheld units will track using 3 satellites, while higher end units can track using up to 12 satellites, and can usually track very well even in the toughest weather conditions. One of the major advantages to GPS units is that they have the ability to store specific locations or landmarks, so that they are always remembered. Most units can store hundreds of locations, which are sometimes referred to as waypoints , including routes and legs or branches off these routes.