The iPhone OS, known as OS X iPhone in its early history, is the operating system developed by Apple Inc. for the iPhone and iPod touch. Like Mac OS X, from which it was derived, it uses the Darwin foundation. iPhone OS has four abstraction layers: the Core OS layer, the Core Services layer, the Media layer, and the Cocoa Touch layer. The operating system takes less than 240 Megabytes of the device's total memory storage. This operating system did not have an official name until the release of the first beta version of the iPhone SDK on March 6, 2008. Before then, Apple marketing literature simply stated that the "iPhone uses OS X," a reference to Apple's desktop operating system, Mac OS X. As of September 28, 2009, there are over 85,000 applications officially available for the iPhone, and 2 billion downloads had been achieved. On September 9, 2009, Apple announced that the version 3.1 of the OS will be free for users who already have OS 3.0.
