Difference between DSI and regular fish finder

Thinking about purchasing two new fish finders one to mount to the trolling motor and another I plan on mounting to the transom. Think I'm going to go with the lowrance x4 for the trolling motor but not sure what I want for the transom lowrance has the mark 5x then also elite-4x color and the elite 4x dsi. My biggest question is can you really tell that much difference with the dsi verses the traditional anyone that could give me some information it would be greatly appreciated.

Lots of information on this topic can be found in the "Fishing Electronics and Trolling Motor" forum in a thread called "Disscussion on Lowrance Elite 5DSI". This might help. Good Luck!!