iOS is derived from MacOS X,which it shares the Darwin foundation, and is a Unix operating system.
 
 
 iOS consist of four Abstract layers are  
Cocoa Touch
 
Media
 
Core Services
 
Core OS 
Core OS
                   Core OS consist of  C API based on unix, not a object oriented. Core OS handles the following functionalities are OSX kerner,Mach 3.0, BSD, Sockets, Security,Power Management, KeyChain Access, Certificates, File System, Bonjour. 
 Core Services 
                                   Core Services classes are Object Oriented.Core Services 
handles the following functionalities are Collections,Core Location, Address Book, Net Services, Networking, Threading, File Access, Preferences, SQLite, URL Utilities.
 Media
                    Media 
handles the following functionalities are Core Audio, OpenAL, Audio Mixing, Audio Recording, Video Playback, JPEG,PNG,TIFF, PDF, Quartz(2D), Core Animation, OpenGL ES.
   Cocoa Touch
                                      Cocoa Touch 
handles the following functionalities are Multie Picker-Touch, Core Motion, View Hierarchy, Localization, Alerts, WebView, Map Kit, Image Picker, Camera, Controls.