iOS

iOS, formerly known as iPhone OS (and Mac OS X Mini), is the operating system for the iPhone, iPod touch, iPad and Apple TV 2G. iOS has four abstraction layers: the Core OS layer, the Core Services layer, the Media layer, and the Cocoa Touch layer. The OS takes ~350MB of the device's total memory storage, this means that users will not get their full storage space.

In iOS 4, it takes up ~800MB of space, ~200MB more than double, probably due to the 2x graphics that have been added for the iPhone 4's Retina display. All of it is stored in the root partition