HDTV sources

The rise in popularity of large screens and projectors has made the limitations of conventional Standard Definition TV (SDTV) increasingly evident. An HDTV compatible television set will not improve the quality of SDTV channels. To get a better picture HDTV televisions require a High Definition (HD) signal. Typical sources of HD signals are as follows:

• Over the air with an antenna. Most cities in the US with major network affiliates broadcast over the air in HD. To receive this signal an HD tuner is required. Most newer HDTV televisions have a HD tuner built in. For HDTV televisions without a built in HD tuner, a separate set-top HD tuner box can be rented from a cable or satellite company or purchased.
• Cable television companies often offer HDTV broadcasts as part of their digital broadcast service. This is usually done with a set-top box or CableCARD issued by the cable company. Alternatively one can usually get the network HDTV channels for free with basic cable by using a QAM tuner built into their HDTV or set-top box. Some cable carriers also offer HDTV on-demand playback of movies and commonly viewed shows.
• Satellite-based TV companies, such as DirecTV and Dish Network (both in North America), Sky Digital (in the UK and Ireland), Bell ExpressVu (in Canada) and NTV Plus (in Russia), offer HDTV to customers as an upgrade. New satellite receiver boxes and a new satellite dish are often required to receive HD content.
• Video game systems, such as the Xbox (NTSC only), Xbox 360, Playstation 2 (Gran Turismo 4) and Playstation 3 can output an HD signal. The Xbox Live Marketplace and Playstation Network services offers HD movies, TV shows, movie trailers, and clips for download to their respective consoles.
• Most newer computer graphics cards have either HDMI or DVI interface, which can be used to output image to HDTV television.
• Two optical disc standards, Blu-ray and HD DVD, can provide enough digital storage to store hours of HD video content.

http://en.wikipedia.org/wiki/High-definition_television