For example, the controller embedded in an elevator tells the motor to move the elevator to different floors, based on buttons that are pushed. A decoder is embedded in a satellite television set-top box (called STB) to read a signal from the dish and send something that a TV understands. Often this type of system must do its work in a specific amount of time. This is called real-time computing. If a set-top box got interrupted to do another task, you would see a bad picture on the TV, for example. A general purpose computer will often have short pauses while it does something else, it is not real-time.