Any television can display digital channels. This includes Freeview, the free digital television service that comprises all the channels from Australia’s free-to-air broadcasters, including the ABC, SBS, Seven Network, Nine Network, Network Ten, Prime, Win and Southern Cross.
When is a set top box necessary?
To watch digital channels, your TV needs to have a digital receiver. Most modern (ditigal) TVs have a digtal tuner built in - but those who still have an analogue television will need a set top box. It converts the digital signals to analogue, so it can be displayed on your screen.
SD or HD?
Whether you choose to have an SD or HD set top box depends on a couple of different things. The main difference between the two lies in their ability to display either standard definition (SD) or high definition (HD) digital television feeds. An SD set top box can only access standard definition channels, while an HD set top box can show both standard definition and high definition channels.
In practical terms, if you're using an analogue TV the biggest difference is that HD set top boxes can receive more channels. HD set top boxes can also be attached to computer monitors in order to use them as HDTV displays.