Analog, high definition and digitial - they are all different kinds of pictures you can watch on television right now! Starting in February 2009, you'll have to have a tv that receives a digital picture, or you won't be watching tv at all.
Digital tv is not necessarily HDTV, or high definition television. HD uses digital technology to dramatically increase the amount of picture information or "resolution".
Today's analog system produces a picture with 440 lines of resolution, but HDTV can produce nearly three times the number of lines. That creates a much sharper picture.
Perhaps the most noticeable difference between HDTV and traditional tv is the shape and size of the screen. For years, tv screens were in a ratio of 4:3, four units wide by three units high; a decision made to accomodate early motion picture formats.
HDTV is radically different: 16 units wide by 9 units high, which is actually closer to the way we see. Unlike traditional 4x3 sets with their picture tubes, HDTV sets can be enormous; some models measuring a whopping 100" across.