iOS devices have different layers that contain unique components responsible for performing specific functions within the application, guaranteeing efficient and safe communication with the device's hardware.

These include:

• The Cocoa Touch layer (or the application layer) is responsible for the application's appearance and how it interacts with users. Plus, it also contains critical iOS components that allow multitasking between applications and using the touchscreen to request commands.
• The Media layer holds all video, audio, and graphic frameworks that allow users to listen to their favorite music or watch movies.
• The Core Services layer contains essential technologies like: the Address book framework, Core Location framework, Social framework, Healthkit framework, and others. These are necessary to support device applications. It doesn't mean your application will need all these components but they are available to be accessed at any time.
• The Core Layer is the closest one to the device hardware. It handles low-level functionalities such as networking, memory, and external accessories.

Due to the layered structure, iOS applications keep functioning effortlessly even if there are certain hardware changes on the device. Plus, the malfunctioning of one layer doesn't affect others, which makes it easier to test and debug each layer.