Many new LCD HDTVs can display images at a 120Hz refresh rate. This simply means the frames from a standard 60Hz source are drawn twice as often, or the frames from 24Hz are displayed 5 times.
With special video processing techniques, such as Samsung's AutoMotion Plus and Sony's MotionFlow, 120Hz LCDs can make motion appear smoother. This means the TV will take the incoming 24Hz or 60Hz signal and calculate new interpolated frames.
It's important to realize that this processing takes place entirely within the 120Hz television; there is no additional data passed along the video cable for 120Hz frame interpolation!
Why are some cables advertised as 120Hz-capable?
Unfortunately, this is nothing more than a marketing gimmick. Motion interpolation and 120Hz display are performed entirely within the TV. There is no need for a special source or cable.
There are currently no HDTVs that can accept a 120Hz signal, nor are there any sources with 120Hz content. A cable offering "120Hz" has no more benefit than any other cable.