All iPods except for the iPod Touch can function in "disk mode" as mass storage devices to store data files but this may not be the default behavior, and in the case of the iPod Touch, requires special software.[citation needed] If an iPod is formatted on a Mac OS computer, it uses the HFS+ file system format, which allows it to serve as a boot disk for a Mac computer. If it is formatted on Windows, the FAT32 format is used. With the release of the Windows-compatible iPod, the default file system used on the iPod line switched from HFS+ to FAT32, although it can be reformatted to either file system (excluding the iPod Shuffle which is strictly FAT32). Generally, if a new iPod (excluding the iPod Shuffle) is initially plugged into a computer running Windows, it will be formatted with FAT32, and if initially plugged into a Mac running Mac OS it will be formatted with HFS+.

To work as a boot disk for a Mac, what file system must an iPod be formatted with?