Set-top box

A set-top box is a small device that adds extra functionality to another media device, often a television. In general, there are different kinds of such devices:

1. Active devices provide a signal to the TV, they do not get any feedback from the TV. Examples of such devices are video game consoles, or DVD players.
2. Passive devices rely on the TV, they don't add any new functionality; they are rare, though
3. Bidirectional devices provide a signal to the TV, but they also get information back. Examples for bidirectional devices are videocassette recorders.

A settuop box for Cable TV

The most important functions of a set top box are media playback (DVD, VHS videos, perhaps interacve as a game console), recording of the data received, and being able to receive data using different channels (for example Satellite TV, TV over internet) or methods (sometimes, signals need to be decrypted first; some people want to watch digital TV on an analogue television).

The evolution of set-top boxes can be traced back to early 1980s, when a cable converter box was required to receive extra analog cable TV channels and convert them to content capable of being displayed on a regular television screen. The cable converter boxes came with a wired or wireless remote control, which helped to switch a channel to a low-VHF frequency for viewing on the TV. Some newer television receivers significantly reduced the need for external set-top boxes but they are still in wide use. Cable converter boxes are sometimes required to descramble premium cable channels and receive interactive services such as pay per view, video on demand and home shopping channels.