What are set top boxes?
Set top boxes (STB) are devices that can receive and decode digital television (DTV) broadcasts so that they can be displayed on analogue televisions, or other display devices which don't have the required tuners built in. Most new televisions come with a digital tuner built in, and as such don't require a set top box to decode terrestrial broadcast 'Freeview' TV.
Set top boxes are also used to receive other types of digital television, including cable TV broadcasts, satellite TV broadcasts, and IPTV (a Foxtel box, for example, is a set top box).
Set top boxes can receive and output either standard definition (SD), or both standard definition and high definition (HD), depending on the type of STB you use. An SD-only set top box won't be able to receive or output HD channels, whereas an HD-capable set top box can receive both, and in most cases can output the signal to any television.
Because analogue broadcasting was completely shut off in most parts of Australia by 2013, a set top box is necessary for television viewers still using CRT televisions who wish to use their current television set to receive digital television broadcast. Set top box prices range from anywhere between about $50 for one with basic features, to over $1,000 for a more sophisticated box which allows you to record, pause and so forth.
How are set top boxes used?
Simpler set top boxes simply allow you to change through channels, and provide information about what's on via an electronic program guide (EPG). Some set top boxes also feature PVR functionality, allowing you to record programs, and to rewind or pause a show while you're watching it - many via an external USB drive or hard disk.
If the set top box has two tuners built in, you can also record one channel while watching another. Also, with some cable and satellite systems an internet-enabled STB will offer some degree of interactivity, and may even let you play simple games.
What variations exist?
The main differences between set top boxes are in what sort of television broadcasts they'll let you receive. The most common type is the one that allows you to pick up free television using a 'normal' antenna. Other types include cable TV set top boxes and satellite TV set top boxes, and IPTV set top boxes.
There are also variations between these types of STBs themselves - mostly in terms of the features and functions they offer.
What are the alternatives?
Most new televisions come with a digital tuner built-in, and as such don't require a separate STB to receive and decode free HDTV signals. You can also buy cards and adapters for computers which will serve a similar purpose, giving you HDTV on your computer screen.
Analogue TV used to be another alternative - but that was completely phased at the end of 2013.
Another alternative is a dedicated web-streaming television feed, which bypasses traditional over-the-air broadcasting altogether.