I know about --><-- that much about Tomtom GPS units, but I do know a bit about general, marine, hand-held and auto GPS units
Most of the time, all that is held in the memory is the data for the maps, not the software that runs the GPS, processes and displays the data, etc, etc, etc.
I suspect the only way to get a Garmin going, is have a dash/window/etc Garmin GPS.
Personally, with the length time I tend to own vehicles, getting an "built in" GPS would be something I would avoid. Electronics is long obsolete by the time I go to replace a vehicle.