What difference does it make that I have two SD cards

Question

I guess I don't really understand the Android storage structure; maybe someone can enlighten me or direct me to a place that does. I have a Galaxy S3, Android 4.0.5, with two 16GB SD cards. So:

1. Does the phone have internal storage other than the SD cards?
2. Under /mnt, I see both sdcard and extSdCard; there is also sdcard under /. I assume this is just a link. But this implies to me that the external sd card is somehow "less important" than the original SD card. Is that true?
3. I would like to use perhaps doubletwist, or some other application, to put my whole iTunes library, which is slightly larger than 16GB, on my phone. Will that application (or any application) insist on having 16gig on one card, or will it just figure it out and put the data wherever it needs to go?
4. The file structure on my sd cards seems pretty complicated, with lots of empty folders. What folders are really needed by the OS, and how can I figure out what is supposed to go in each?

I guess this comes down to two questions: 1) how can I figure out what the principles are behind the Android file system, and 2) do applications care that there are two cards, or do they/can they treat it as a single disk?

Thanks.

Answer 1

By the sound of it, its like as if the handset is in fact a 16GB model variant, if so, then the so-called sdcard is treated as internal storage i.e. sdcard, and the external SDCard is symbolically linked to extSdCard.

That is the way Google are doing it now, and doing away with having external SDCard's... :)

No its not true that one is "more" important than the other, its just a way of increasing internal storage capacity for apps and media etc, the external SDCard acts as a "overflow" bucket once the storage space on the internal sdcard gets maxed out.