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.
IPhone be accessed by a hardware button below the screen on all models expect for the iPhone X where the user must swipe up. The original iPhone contained the following apps: Messages (SMS and MMS messaging), Calendar, Photos, Camera, YouTube, Stocks, Maps (Google Maps), Weather, Voice Memos, Notes, Clock, Calculator, Settings and iTunes (store). The App Store was introduced for the iPhone 3GS and iPhone 4. Compass, FaceTime and GameCenter were added in iOS 4 and 4.1 respectively. In iOS 5, Reminders and Newsstand were added, and the iPod application was split into separate Music and Videos applications. iOS 6 added