All the iDevices use HFSX as their file system, a variant case of HFS+. Within the same folder, then, it is possible to store two or more files with the same name, but different from the case of each individual character (for example,
HFS Plus (or HFS+) is the file system developed by Apple to replace, from Mac OS 8.1, HFS as the default file system for Mac computers. In Apple's official documentation, it is called Mac OS Extended.
HFS+ is an improved version of HFS, which allows the user to support larger files (thanks to block addresses of 32 bits instead of 16 bits) and uses Unicode for the names of file system objects (files and folders), thus allowing up to 255 characters for each. Until ...