The UIDevice class provides a singleton instance representing the current device. From this instance you can obtain information about the device such as assigned name, device model, and operating-system name and version. Available in iOS 2.0 and later
UIDevice instance is used to detect changes in the device’s characteristics, such as physical orientation. You get the current orientation using the orientation property or receive change notifications by registering for the UIDeviceOrientationDidChangeNotification notification. Before using either of these techniques to get orientation data, you must enable data delivery using the beginGeneratingDeviceOrientationNotifications method.
When you no longer need to track the device orientation, call the endGeneratingDeviceOrientationNotifications method to disable the delivery of notifications.
Source: UIDevice Class reference
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