iOS (originally iPhone OS) is a mobile operating system created and developed by Apple Inc. and distributed exclusively for Apple hardware. It is the operating system that presently powers many of the company's mobile devices, including the iPhone, iPad, and iPod touch. It is the second most popular mobile operating system in the world by sales, after Android. iPad tablets are also the second most popular, by sales, against Android since 2013, when Android tablet sales increased by 127%.

Originally unveiled in 2007, for the iPhone, it has been extended to support other Apple devices such as the iPod Touch (September 2007), iPad (January 2010), iPad Mini (November 2012) and second-generation Apple TV onward (September 2010). As of January 2015, Apple's App Store contained more than 1.4 million iOS applications, 725,000 of which are native for iPads. These mobile apps have collectively been downloaded more than 100 billion times.

The iOS user interface is based on the concept of direct manipulation, using multi-touch gestures. Interface control elements consist of sliders, switches, and buttons. Interaction with the OS includes gestures such as swipe, tap, pinch, and reverse pinch, all of which have specific definitions within the context of the iOS operating system and its multi-touch interface. Internal accelerometers are used by some applications to respond to shaking the device (one common result is the undo command) or rotating it in three dimensions (one common result is switching from portrait to landscape mode).

iOS shares with OS X some frameworks such as Core Foundation and Foundation Kit; however, its UI toolkit is Cocoa Touch rather than OS X's Cocoa, so that it provides the UIKit framework rather than the AppKit framework. It is therefore not compatible with OS X for applications. Also while iOS also shares the Darwin foundation with OS X, Unix-like shell access is not available for users and restricted for apps, making iOS not fully Unix-compatible either.

Major versions of iOS are released annually. The current release, iOS 9.2, was released on December 8, 2015. In iOS, there are four abstraction layers: the Core OS layer, the Core Services layer, the Media layer, and the Cocoa Touch layer. The current version of the operating system (iOS 9), dedicates around 1.3 GB of the device's flash memory for iOS itself.  It runs on the iPhone 4S and later, iPad 2 and later, iPad Pro, all models of the iPad Mini, and the 5th-generation iPod Touch and later.

History

In 2005, when Steve Jobs began planning the iPhone, he had a choice to either "shrink the Mac, which would be an epic feat of engineering, or enlarge the iPod". Jobs favored the former approach but pitted the Macintosh and iPod teams, led by Scott Forstall and Tony Fadell, respectively, against each other in an internal competition, with Forstall winning by creating the iPhone OS. The decision enabled the success of the iPhone as a platform for third-party developers: using a well-known desktop operating system as its basis allowed the many third-party Mac developers to write software for the iPhone with minimal retraining. Forstall was also responsible for creating a software developer's kit for programmers to build iPhone apps, as well as an App Store within iTunes.

The operating system was unveiled with the iPhone at the Macworld Conference & Expo, January 9, 2007, and released in June of that year. At first, Apple marketing literature did not specify a separate name for the operating system, stating simply what Steve Jobs claimed: "iPhone runs OS X" and runs "desktop applications" when in fact it runs a variant of [Mac] OS X, that doesn't run OS X software unless it has been ported to the incompatible operating system. Initially, third-party applications were not supported. Steve Jobs' reasoning was that developers could build web applications that "would behave like native apps on the iPhone".On October 17, 2007, Apple announced that a native Software Development Kit (SDK) was under development and that they planned to put it "in developers' hands in February" On March 6, 2008, Apple released the first beta, along with a new name for the operating system: "iPhone OS".

On September 5, 2007, Apple released the iPod Touch, which had most of the non-phone capabilities of the iPhone. Apple also sold more than one million iPhones during the 2007 holiday season. On January 27, 2010, Apple announced the iPad, featuring a larger screen than the iPhone and iPod Touch, and designed for web browsing, media consumption, and reading iBooks.

In June 2010, Apple rebranded iPhone OS as "iOS". The trademark "IOS" had been used by Cisco for over a decade for its operating system, IOS, used on its routers. To avoid any potential lawsuit, Apple licensed the "IOS" trademark from Cisco.

By late 2011, iOS accounted for 60% of the market share for smartphones and tablets By the end of 2014, iOS accounted for 14.8% of the smartphone market and 27.6% of the tablet and two-in-one market. As of February 2015, StatCounter reported iOS was used on 23.18% of smartphones and 66.25% of tablets worldwide

IOS 1-3

In June 2007, Apple released the first version of what became iOS – concurrently with the first iPhone. The final 1.x series release was 1.1.5, released shortly after version 2.0.

July 11, 2008 saw the public release of iPhone OS 2.0, with upgrades through version 2.2.1 made available.

June 17, 2009 was the release date for iPhone OS 3.0. It was updated through (and including) version 3.1.3 (release date February 2, 2010).The first generationiPod Touch and iPhone have iPhone OS 3.1.3 as their newest available version. All iOS versions from 3.2 until 4.0 were made specifically for the iPad.

On June 21, 2010, iOS 4.0 (formerly iPhone OS) was released to the public and was made available only to the iPod Touch and iPhone. iOS 4.0 was announced to have over 1500 new APIs for developers, with the highly anticipated multitasking feature.The iPod Touch (2nd generation) and iPhone 3G have iOS 4.2.1 as the final version available. Nevertheless, many features are not available for the iPhone 3G or iPod Touch (2nd generation), such as multitasking and home screen backgrounds. iOS 4.2 is the first version to bring major feature parity to the iPhone and iPad. The release of the CDMA iPhone for Verizon Wireless saw a branching of iOS. The 4.2 version sequence continued for the CDMA phone while 4.3 was released for all other products.

On June 6, 2011, Apple previewed iOS 5, Apple TV 4.4 beta and the iOS SDK 5 beta along with iCloud beta among other products. This update introduced iMessagechat between devices running iOS 5, a new notification system, Newsstand subscriptions, Twitter integrated into iOS, Reminders app, Enhancements to AirPlay, full integration with iCloud and over 200 new features. iOS 5.0 supports all iPad models, iPhone 3GS, iPhone 4 GSM & CDMA, iPhone 4S, and the iPod Touch (3rd & 4th generation).

iOS 5 had only three minor additions, 5.0.1, 5.1, and 5.1.1, which were all provided as OTA and iTunes software updates.

Apple concurrently provides the same version of iOS for the comparable model of iPhone and iPod Touch, usually devices released in the same calendar year. iPhone users receive all software updates for free, while iPod Touch users paid for the 2.0 and 3.0 major software updates. As of iOS 4.0, Apple no longer charges money for iPod Touch updates.

As of October 23, 2011, two versions of iOS were never released. iPhone OS 1.2, which after the first beta was replaced by a 2.0 version number; the second beta was called 2.0 beta 2 instead of 1.2 beta 2. The other was iOS 4.2, replaced with 4.2.1 due to a Wi-Fi bug in 4.2 beta 3, causing Apple to release 2 golden masters (4.2 GM and 4.2.1 GM).One version of iOS was pulled back by Apple after being released. iOS 8.0.1 was pulled back by Apple because cellular service and Touch ID were disabled on iPhone 6 and iPhone 6 Plus.

Source:

https://en.wikipedia.org/wiki/IOS