Android File Structure
From Just Solve the File Format Problem
Note: this is very work in progress.
|Stores most system files. It can be accessed with file manager apps on an unrooted device, and written with root permission. An option in recovery mode can mount this partition to a PC, Macintosh, Chromebook, iDevice, or even another Android device.
|Stores most user data. This is the hardest partition to access without root, hardware hacks, rootkit malware, or expensive forensic tools
|a root-point for shared storage, includes mounted sd cards and usb otgs and also internal storage.
|Stores regular storage that can be accessed by your local file manager app. This includes photos, music, and downloads.
|Stores app data and cache.
|Shortcut to /data/user/0/
|Stores miscellaneous data.
|Stores WiFi data including passwords.