to external OEM companies, maintaining a high degree of control over the end product. The iPhone contains most of the hardware parts of a typical modern smartphone. Some hardware elements, such as 3D Touch and the Taptic Engine, are unique to the iPhone. The main hardware of the iPhone is the touchscreen, with current models offering screens of 4.7 inches and larger. All iPhones include a rear-facing camera; the front-facing camera dates back to the iPhone 4. The iPhone 7 Plus introduced multiple lenses to the rear-facing camera. A range of sensors are also included on the device, such as a proximity sensor, ambient light sensor, accelerometer, gyroscopic sensor, magnetometer, facial recognition sensor or fingerprint sensor (depending on the model) and barometer. In 2022, Apple added satellite communications to the iPhone, with the release of the iPhone 14 and iPhone 14 Pro. Software Operating system The iPhone runs iOS. It is based on macOS's Darwin and many of its userland APIs, with Cocoa replaced by Cocoa Touch, and AppKit replaced by UIKit. The graphics stack runs on Metal, Apple's low-level graphics API. The iPhone comes with a set of bundled applications developed by Apple, and supports downloading third-party applications through the App Store. Apple provides free updates to iOS over-the-air, or through Finder and iTunes on a computer. Major iOS releases have historically accompanied new iPhone models. App Store and third-party apps At WWDC 2007 on June 11, 2007, Apple announced that the iPhone would support third-party Ajax web applications that share the look and feel of the iPhone interface. On October 17, 2007, Steve Jobs, in an open letter posted to Apple's "Hot News" weblog, announced that a software development kit (SDK) would be made available to third-party developers in February 2008. The iPhone SDK was officially announced and released on March 6, 2008. The App Store was launched with the release of iPhone OS 2.0, on July 11, 2008. Apple requires all third-party apps to be downloaded from the App Store, with exceptions for ad-hoc apps used within enterprises. Developers must pay a yearly $99 fee as part of Apple's Developer Program; if their membership expires, their apps are removed from the App Store, though existing users retain the ability to redownload the app. Developers can release free apps, or paid apps for which Apple takes a 30% cut of proceeds. Developers earning less than $1 million in