I have an old Magellan 6000 GPS which uses C-Map cards. You should google C-Map to get a better idea what "NT" is. C-Map makes various "Cards" that plug into varoius GPS Units. ALL the map data is ON the plug in card.
A couple of years ago I lost one of my cards..different cards, different areas, so I took a ride out to Cape Cod where C-Map is located to get a new replacement card. The new replacement plugged into the GPS OK but the Magellan GPS didn't have enough memory to run the NEW card because they had added so much additional data.
In addition: C-Map did NOT keep backup software for the "Old" card that I lost. So I was out of luck.
NB