After tons of posts on this subject I was directed to the following info! Too my knowledge it is available on most of the Garmin's including my 3590.
The following is quoted from this forum!
For many reasons, users will want to save this info. That is why I put it as a new thread to find easier.
See the post about halfway down this thread: http://forums.gpsreview.net/viewtopic.php?t=21019
Make NUVI DIR & Files visible for Backup
1. To make all of Nuvi files visible you must unhide protected files via Win7 like any other HD.
2. Start NUVI by itself and go to Volume Screen.
3. Press the upper right hand corner of screen for 10 seconds.
4. The Developers Screen will pop up
5. Scroll down to MTP SETTINGS
6. Change from AUTO DETECT to MASS STORAGE
7. Shut down NUVI and hookup to Computer USB cable
8. Start NUVI and it should recognize it is hooked up to the computer.
9. Explorer will now see all files in ROOT directory and the .System directories.
BTW, have you backed up your Nuvi? If not, then this would be a good time to do it. Could save a lot of grief later if you have a problem