IPod games are in the form of .ipg files, which are actually .zip archives in disguise. When unzipped, they reveal executable files along with common audio and image files, leading to the possibility of third party games. Apple has not publicly released a software development kit (SDK) for iPod-specific development. Apps produced with the iPhone SDK are compatible only with the iOS on the iPod Touch and iPhone, which cannot run clickwheel-based games. 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.
VoiceOver iPod Shuffle VoiceOver is intended to be used by everyone, disabled or not. A few months later, with the release of the iPhone 3GS, VoiceOver was added to iOS. When the iPod Touch was upgraded to match the hardware of the iPhone 3GS (in iPod touch's third generation), it also gained VoiceOver capability. The iPad, since its introduction, has also had VoiceOver capability. VoiceOver on iOS interacts with the user by using various "gestures," different motions one makes with one or more fingers on the display. Many gestures are location-sensitive—for example, sliding one's finger around the screen will reveal the