Q: I would like to back up the back up file that my iPhone has, so if I lose my hard drive, I can still recover the iPhone. Where is the back up file located? How does iTunes make this file?
A: iTunes makes a backup of your iPhone’s content each time you sync your iPhone, but unfortunately it tends to store this backup in a rather non-intuitive location, making it obvious that Apple never really intended for end-users to find these files directly (although they will of course be backed up as part of a full system backup).
For Windows users, you should be able to find your iPhone backup files in the Application Data\Apple Computer\Mobile Sync\Backup folder under your user profile (ie, C:\Documents and Settings\(yourusername)). Note that the “Application Data” folder is a hidden folder by default, so you may need to reveal hidden and system folders in your Windows Explorer options in order to see it.
For Mac users, your iPhone backups are stored in your home folder’s Library/Application Support/MobileSync/Backup folder.
The actual backup itself is stored in a sub-folder with a name that is generated based on your device’s internal ID. If you have synchronized multiple iPhone or iPod touch devices with the same iTunes library, there may be multiple folders located here.
Note that the backup files themselves are not encrypted in any way, and although they are not intended to be accessible to the casual user, it is possible for a knowledgeable user to access the data within these files quite easily.
For the technically curious, the files are in an Apple binary PLIST format with the data inside base-64 encoded.
The data stored in the backup is quite comprehensive, particularly with newer iPhone firmware versions, having been expanded to include even information such as YouTube bookmarks and photos that you have taken with the iPhone’s camera. In fact, at this point about the only data that is not included in these backups is your actual media content, which is synced from your iTunes library anyway.
Simply backing up the entire content of the MobileSync\Backup folder should suffice to ensure that you have an offline backup of your iPhone’s data, and in the event that you need to move it to a different computer or restore a crashed hard drive (and iPhone), you can simply put this data back in the same place in a new iTunes installation, and it will be available to be restored to your iPhone.