The interface is based around the home screen, a graphical list of available applications. iPhone applications normally run one at a time. Starting with the iPhone 4, a primitive version of multitasking came into play. Users could double click the home button to select recently opened applications. However, the apps never ran in the background. Starting with iOS 7, though, apps can truly multitask, and each open application runs in the background when not in use, although most functionality is still available when making a call or listening to music. The home screen can be accessed by a hardware button below the screen on the iPhone 8 and earlier. iPhone X and later models, with the exception of the second-generation iPhone SE, instead use touch-based gestures.