The iPhone OS is the operating system developed by Apple Inc. for the iPhone and iPod touch. 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. iPhone OS has four abstraction layers: the Core OS layer, the Core Services layer, the Media layer, and the Cocoa Touch layer. Some multitasking is permitted, but it is not obtrusive or obvious, and it is limited to Apple's own applications. OpenGL ES is used as graphics API. As of Nov. 4, 2009, there are over 100,000 applications officially available for the iPhone, and 2 billion downloads had been achieved. On September 9, 2009, Apple announced version 3.1 of the iPhone OS.