Standard TV
If you watch a high definition (HD) program (16:9 ratio) on a standard TV (4:3 ratio), it will place black bars at the top and bottom of the screen where there is no picture. Sometimes an HD channel will show a standard program (with black bars on the sides), so if you are watching on a standard TV, you will see black bars all the way around. If this happens, switch to standard broadcast for that network.
HD TV
If you watch a standard definition channel on your HD TV, it will place black bars at the sides of the screen where there is no picture. Sometimes a standard channel may show a widescreen program (with black bars at the top and bottom), so if you are watching on your HD TV, you will have black bars all around your screen. Some HD TVs have a zoom function for these programs, so they can be set to fill the screen without distortion.