A set-top box is a small device that generally sits on top of a television set and converts video and audio signals. Set-top boxes are common with satellite and cable television systems.
Set-top boxes often do more than simply convert signals. In the cases of cable and satellite television, the boxes are also generally responsible for unscrambling premium channels. Satellite boxes often use an access card to determine which channels should be unscrambled, while cable television set-top boxes often rely on a specific signal sent by the cable television provider. Other types of modern set-top boxes include digital media streaming devices.