Digital TV is broadcast as a digital signal through various mediums. Over the air (OTA), cable and satellite are the three methods by which most people receive digital television signals. You need some additional hardware to decode the digital signal and display it on a television or computer monitor.
This hardware can be a PCI card to install in a PC or an external device box connected to your aerial, cable or satellite dish.
Some countries are already in the process of converting all broadcast television to a digital format. Starting in 2008 some parts of the UK will no longer have analogue TV broadcasts.
Digital Television formats include ATSC, DVB, DCII, and other formats which MythTV treats as pure MPEG-2 or MPEG-4 streams. On Linux, most DTV hardware in MythTV relies on the confusingly name "DVB" family of drivers.