iPhone OS runs on iPhone and iPod touch devices.
Hardware devices are managed by iPhone OS and provides the technologies needed for implementing native applications on the phone.
The OS ships with several system applications such as Mail, Safari, Phone, which provide standard services to the user.
iPhone SDK is available with tools and interfaces needed for developing, installing and running custom native applications.
Native applications are built using the iPhone OS’s system frameworks and Objective-C language and run directly on iPhone OS.
Native applications are installed physically on a device and can run in presence or absence of network connection.
It is similar to MacOS X architecture
It acts as an intermediary between the iPhone and iPod hardware an the appearing applications on the screen
The user created applications never interact directly with the appropriate drivers, which protects the user applications from changes to the hardware.