以下是iOS模拟器下，文件的组织形式，在iOS Device 上的文件组织形式也是这样的。
iOS 将第三方程序储存在 Applications 文件夹下，各个程序的所有文件都在其 globally unique identifiers (GUIDs) 的文件下，GUID 文件夹即是程序的沙盒。
Documents: Your application stores its data in Documents, with the exception of NSUserDefaults-based preference settings.
Library: NSUserDefaults-based preference settings are stored in the Library/Preferences folder.
tmp: The tmp directory offers a place where your application can store temporary files. Files written into /tmp will not be backed up by iTunes when your iOS device syncs, but your application does need to take responsibility for deleting the files in /tmp once they are no longer needed, to avoid filling up the file system.
Getting the Documents Directory
Here’s some code to retrieve the path to the Documents directory:
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
Getting the tmp Directory
NSString *tempPath = NSTemporaryDirectory();
注：
大部分内容摘自《Beginning iPhone 4 Development Exploring the iOS SDK》