A 'High definition TV' is defined as a television screen which can display vertical resolution lines numbering 720 and above. Currently there are four standard resolution formats for HD, which are listed below.

1. 720p - there are XGA, HD Ready and WXGA variants.
2. 1080i - the 'i' stands for interlaced, a non standard form of HD.
3. 1080p - the standardised version of the 1080 line display.
4. 2160p - currently only used by digital cinema initiatives 'DCI'.

Below, for your convenience, is listed the attributes of each of the formats,

Native resolution (width x height)

1. 720p - 1280 × 720
2. 1080i - 1280 × 1080
3. 1080p - 1920 × 1080
4. 2160p - 3840 × 2160

Total amount of pixels supported

1. 720p - 921, 600
2. 1080i - 1, 382, 400
3. 1080p - 2, 073, 600
4. 2160p - 8, 294, 400

Aspect ratio

1. 720p - 16:9
2. 1080i - 16:9
3. 1080p - 16:9
4. 2160p - 16:9

Currently, you cannot purchase a TV with a HD format of 2160p. The technology does exist, but at the time of writing it's only been introduced into cinema complexes. Estimates suggest it could be five years until consumers are able to purchase a 2160p television.

Only BSkyB (2009), in the UK, offer a dedicated high definition television channel. Expect this to be expanded upon, as the ITV and the BBC are beginning to broadcast many of their premium programming in HD.

The production studios in the UK are still digesting the SMPTE 296M, 292M, 259M and 344M signal protocols. They can transport uncompressed digital data. The BBC has also been experimenting with the compression codec, 'MPEG-4 AVC'.

However, at present, it appears to be a work in progress, with terrestrial viewers waiting with baited breath for the HD revolution.