A set-top box is necessary to television viewers who wish to use their current analog television sets to receive digital broadcasts. It is estimated that 35 million homes will use digital set-top boxes by the end of 2006, the estimated year ending the transition to DTV.
In the Internet realm, a set-top box is really a specialized computer that can "talk to" the Internet - that is, it contains a Web browser (which is really a Hypertext Transfer Protocol client) and the Internet's main program, TCP/IP. The service to which the set-top box is attached may be through a telephone line as, for example, with WebTV, or through a cable TV company like TCI.
In the DTV realm, a typical digital set-top box contains one or more microprocessors for running the operating system, possibly Linux or Windows CE, and for parsing the MPEG transport stream. A set-top box also includes RAM, an MPEG decoder chip, and more chips for audio decoding and processing. The contents of a set-top box depend on the DTV standard used. European DVB-compliant set-top boxes contain parts to decode COFDM transmissions while ATSC-compliant set-top boxes contain parts to decode VSB transmissions. More sophisticated set-top boxes contain a hard drive for storing recorded television broadcasts, for downloaded software, and for other applications provided by your DTV service provider.
Digital television set-top boxes are used for satellite, cable, and terrestrial DTV services. They are especially important for terrestrial services because they guarantee viewers free television broadcasting.
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.
Set-top boxes can be divided into several categories ranging from simple boxes that receive and descramble incoming AV signals, to complex units delivering a slew of services such as videoconferencing, home networking, IP telephony, video on demand and satellite broadband TV services.
The set-top boxes can be broadly classified into the following types: