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.