iOS is Apple's mobile operating system developed originally for the iPhone, and later deployed on the iPod Touch and iPad as well. It is derived from Mac OS X, with which it shares the Darwin foundation, and is therefore a Unix-like operating system, by nature. In iOS, there are four abstraction layers: the Core OS layer, the Core Services layer, the Media layer, and the Cocoa Touch layer. The operating system uses roughly 500 megabytes of the device's storage.
Version 4, announced in April 2010, introduced multitasking as well as several business-oriented features, including encryption for email and attachments. At the WWDC 2010 keynote on June 7, 2010, Apple announced that iPhone OS had been renamed iOS. Apple licenses the trademark for "iOS" from Cisco Systems (who own IOS), the same company with which Apple had earlier settled a dispute over the "iPhone" trademark.
iOS 4 was released on June 21, 2010, three days before the iPhone 4. Staggering product launches reduces strain on Apple's servers. iOS 4 is the first version of the OS to be a free upgrade on the iPod touch; Apple had charged $9.99 for earlier upgrades. Apple previously announced that iPad users with 3.x software would receive a free upgrade to the next major (4.x) release.
New features of ios4 are:
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