For security purposes, an iOS app has limited a number of places where it can write its data. When an app is installed on a device (either from iTunes or the App Store), the system creates a number of containers for the app. These containers represent the universe for that app and contain everything the app can access directly. Table 1-1 lists some of the important subdirectories inside these containers and describes their intended usage. This table also describes any additional access restrictions for each subdirectory and points out whether the directory’s contents are backed up by iTunes