Another Suggestion.
Take a Blank USB Thumb Drive (Fat32) >= 8GB
Copy your Whole Nuvi Drive to the Thumb Drive (including the .system hidden folder)
Update as Normal
Now you have all the updated files from Garmin on the USB Drive.
Garmin will delete the files that you don't need anymore.
Next Step is to copy back to your Nuvi.
Advantages of this method.
You now have an off site Backup of your Nuvi files. (In Case your computer crashes.)
You can use this Drive with Basecamp instead of always having to plug in your Nuvi.
Bookmarks