This is actually a comparison of two different things, but it is very easy to confuse these definitions with "digital this" and "high-definition that" flying around in the marketplace.

"Digital Television" is a phrase used to describe a type of broadcast, while "High-Definition" is used to describe the format of the broadcast display. It is not absolutely necessary for a high-definition television to display a digital broadcast, nor is it absolutely necessary for high-definition displays to be broadcast digitally. It is entirely possible, although slightly impractical, to broadcast a high-definition program using analog equipment, and at the same time it is not only possible, but common to broadcast standard resolution programming digitally.

There are probably a fair number of people who purchased fairly expensive high-definition-compatible televisions that have no idea whether they are watching a digital broadcast, a high-definition broadcast or an analog broadcast, and since high-definition digital broadcasts are still a tiny fraction of the total amount of programming available, it is more likely than not, at least for those who are not technically aware of the distinctions between all of the standards and formats, they are not seeing the maximum capability of their television equipment for any given program.

It will become easier soon. As analog broadcasting is phased out, and digital broadcasts become standard, the question of what kind of broadcast is being received will no longer be relevant. For the most part, people will not notice any obvious difference between digital and analog broadcasts, except that interference will no longer involve snow, ghosting or any other "analog-type" artifacts.

Another consideration with display formats is the frame rate. A frame rate is simply the number of times the display is refreshed every second. Films are shown at a rate of 24 frames per second, while many high-definition televisions are capable of displaying signals at rates up to 60 frames per second.

The difference between high-definition and standard definition, however, is quite dramatic since high-definition televisions are capable of displaying up to ten times the amount of visual information as a standard analog display. This is not limited only to pixels. A high-definition signal has sharper colors due to a much more substantial amount of bandwidth dedicated to color displays, and it includes native support for 5:1 Dolby Digital AC-3 surround sound, which at the very least should be distinguishable from the two-inch speaker on the side of the old RCA black-and-white.