iOS is an operating system for the iPhone’s (an Apple Inc Product). It is derived from core OS X technologies ( an OS for MAC pc) .The iOS includes the OS X Kernel , BSD Sockets for Networking  and objective-C and C/C++ compilers for native performance. iOS 7.0 is the latest release of iOS on June 10 2013.


The iOS has the layered architecture, different layers are in the below figure.

Cocoa Touch is a UI framework for building software programs to run on the iOS operating system (for the iPhone, iPod Touch, and iPad) from Apple Inc.
Cocoa Touch mainly contains the classes implemented  in Objective-C, an object-oriented language that is compiled to run at incredible speed, yet employs a truly dynamic runtime making it uniquely flexible. Because Objective-C is a superset of C, it is easy to mix C and even C++ into your Cocoa Touch applications.
The framework’s of this layer provides provide the basic  app infrastructure and support for the key technologies ( .i.e Multitasking ,touch-based input, push notification and many  high level system services.)
UIKit Framework: This frame work provides the crucial infrastructure for implementing graphical ,event driven, apps in iOS.
The Media layer contains the graphics, audio, and video technologies you use to implement multimedia experiences in your apps. The technologies in this layer make it easy for you to build apps that look and sound great.
The technologies of this layer are listed as below:


Core Services Layer:

This Layer contains basic system services for apps. Core Foundation and Foundation Frameworks are the key services provided by this layer, which define the basic types that all apps use it also has the technologies which supports the features like location, iCloud,social media and networking.
Some of the High-Level Features and Frameworks provided by this layer are:

This layer contains the low-level features on basis of which the other high-level features are built.Even though we do not use any of these features directly in our  apps ,they used by the frameworks which are used by our application.We can make use of these features when we need to implement the security features  or communicating with an external hardware accessory.
Frameworks provided by this layer are: