Receiver device that processes an incoming signal from a satellite dish, aerial, cable, network or telephone line.
Set-top box, sometimes abbreviated to set-top or STB, is a somewhat misleading term as the device is not necessarily placed on top of the television set and is not necessarily a box.
The term originates from cable television receivers, which were originally analogue tuners that traditionally sat above or sometimes below the television.
The set-top box may have some front panel controls but is typically operated through a remote control aimed an an infra-red receiver on the front of the box.
A digital set-top box receives, decodes and decompresses digital data to produce audio and video signals that can be displayed.
Smaller devices may be little larger than a small book and are sometimes known as digital television adapters or converters.
In the case of an Integrated Digital TV, sometimes referred to as an IDTV or simply a digital television, the capability of the digital receiver is included in the display device.
Essentially a custom computer system, the processing power of the set-top box can vary considerably from basic boxes with limited capabilities to more advanced systems with multiple decoders and sophisticated features.
The set-top box typically provides access to some form of interactive Electronic Programme Guide or EPG which offers details of programming available on each channel.
Interactive applications may also be downloaded to execute on the set-top box. These are typically broadcast as digital data together with the programme material or delivered to the set-top box on demand. Such applications are generally held in memory and are not retained when changing channel or turning off the set-top box.
The set-top box may have a return path or back channel to allow two-way communication and interaction. This is typically provided over a cable television system or using a built-in modem and a standard telephone connection. The set-top box may optionally be connected over a network.
The basic functionality of the set-top box operating system software is stored in non-volatile firmware. This may be capable of being upgraded by a system software update, sometimes referred to as an over-air download.
In some models the set-top box may provide local storage of material on a hard disk, in which case it may be known as a personal video recorder (PVR) or digital video recorder (DVR). Some devices may also include a DVD player or recorder.
The set-top box may provide a connection to a personal computer or home media centre. Some higher end devices are essentially personal computers and the boundary between television devices and computers is increasingly blurred as consumer electronics products converge.