What fubction does an SD card serve?

[Green-ee]

I'm very happy with the Zumo XT and have put many miles on using it. When new I installed a 32 GB card as instructed formatted to FAT 32. Now, 2-3 years later there's nothing on the card other than .System file, Garmin file folder, and Id. 352 KB used, 29.7 free. I would have thought that previous trip data might have been stored in the card but nothing shows. Is this card just for music downloads, or what else does it do?

[Mzokk]

Music, storing routes, alternative mapsets, transfer of routes to other garmin devices are a few of the uses.

[Peobody]

I use it for music but more importantly, to store routes. The XT can modify a route file that is in internal storage but will never modify a route file that is on the SD card. For that reason, some of us prefer to transfer planned routes to the SD card and then use the XT import function to get them into internal storage. Should the one in internal storage get modified, deleting it and then re-importing from the card is a means of recovery.

FWIW, my experience with the XT modifying a route file has been the result of inadvertently changing a route point from shaping to via or vice versa, I don't remember which. This caused a recalculation of the route which included a moved route point and a very different route from what I had created in Basecamp. The route file itself was modified to contain these changes.

[FrankB]

I use the SD-Card to store (custom) OSM maps. They can be quite large, and putting them on the internal storage would just not fit.
I also use it to store custom POI (GPI files)