Is there an industry standard file system cards are formatted with (when you first get them, and/or after a camera formats them)? FAT32, FAT16?
They're formatted with FAT16 or FAT32 (FAT32 is required for card sizes >2GB), and have a fairly specific (though simple) directory structure something like this:
ROOT --- DCIM -+- ###ABCDE | +- ###ABCDE | ...
### is from 100-999, and need not be consecutive. ABCDE is free text.
This structure won't be recreated if you format on a computer, but an in-camera format will usually construct it (or it will be built as required on a blank card).
There are similar standards for file names, and it's all specced out in detail by the Design Rule for Camera File System, which you can read in full here (PDF):
The SD standard formally requires
- FAT16 for regular SD cards
- FAT32 for SDHC
- FAT64 ("exFAT") for SDXC
those formats are indeed to be used by the in-camera format function.
The latter choice has long been under fire by open source activist both due to strict licensing of the exFAT specifications - thus its poor support on anything that's not a recent Windows, Mac OS X or embedded system - and due to it being an allegedly less safe system (saving only one copy of the directory index) although this weakness is less critical on a write/read/reformat workflow as suggested by most camera manufacturers, and followed by pros and amateurs who don't keep their photos for future in-camera playback.