iPhone OS 1
First iteration of Apple's touch-centric mobile operating system. No official name is given on its initial release; Apple marketing literature simply stated the iPhone runs a version of Apple's desktop operating system, OS X.On March 6, 2008, with the release of the iPhone software development kit (iPhone SDK), Apple named it iPhone OS (they went on to rename it "iOS" on June 7, 2010). Support of iPhone OS 1 ended in 2010.
iPhone OS 2
iPhone OS 2, the second major release of iOS, became available on July 11, 2008 with the release of the iPhone 3G. Devices running 1.x are upgradable to this version. This version of the OS introduces the App Store, making third-party applications available to the iPhone and iPod Touch. Prior to the public release of iPhone OS 2.0, Apple held a keynote event to announce the iPhone OS Software Development Kit ("SDK") to developers. Support of iPhone OS 2 has ended in 2011.
iPhone OS 3
Main article: iPhone OS 3 iPhone OS 3.0 became available with the iPhone 3GS. It was released on June 17, 2009. This release added features such as copy and paste, and MMS. Not all features were available on the original iPhone. Devices running iPhone OS 2.x were upgradeable to this software. The final release supported on the original iPhone and iPod Touch is iPhone OS 3.1.3.The iPad was introduced with iOS 3.2.Support of iPhone OS 3 has ended in late 2012.
iPhone OS 4
Main article: iOS 4 iOS 4 was made available to the public for the iPhone and iPod Touch on June 21, 2010. This is the first major iOS release to drop support for some devices (original iPhone and iPod Touch) and that iPod Touch users do not have to pay for.
The iPhone 3G and iPod Touch (2nd generation) have limited features, including lack of multitasking capabilities and the ability to set a home screen wallpaper, while the iPhone 4, iPhone 3GS, iPod Touch (3rd & 4th generation) have all features enabled, such as multitasking. The iPhone and iPod Touch (1st generation) cannot run iOS 4.0 and above.
iOS 4.2.1, released November 22, 2010, added iPad compatibility. It was the initial release on the iPad 2. It also was the last version to support iPhone 3G and iPod Touch (2nd generation). iOS 4.2.1 replaced iOS 4.2 due to a Wi-Fi bug in iOS 4.2 beta 3, causing Apple to release 2 golden masters (4.2 GM and 4.2.1 GM).
iPhone OS 5
Main article: iOS 5 iOS 5 was previewed to the public on June 6, 2011. It was released for iPhone 3GS, iPhone 4 (GSM and CDMA), iPhone 4S, iPod Touch (3rd & 4th generation), iPad, and iPad 2 on October 12, 2011.
iOS 5.1.1 is the final release supported for the iPad (1st generation) and iPod Touch (3rd generation).
iPhone OS 6
Main article: iOS 6 iOS 6 was announced and previewed on June 11, 2012 during Apple Worldwide Developers Conference (WWDC) 2012, and its release was stated as Fall 2012. Following the pattern of prior iOS releases, some older devices were no longer supported, specifically the iPod Touch (3rd generation), and the iPad (1st generation). Supported devices include the iPhone 3GS and later; the iPod Touch (4th generation) and later; and the iPad 2 and later.iOS 6 has limited support on the iPhone 3GS, iPad 2, and iPod Touch (4th generation).
On September 12, 2012 at San Francisco's Yerba Buena Center for the Arts, among other items unveiled, Apple announced three iOS-related items: the next generation iPhone 5, the redesigned iPod Touch (5th generation), and the announcement of the release of iOS 6.0 the following week.
iOS 6 was released to the public on September 19, 2012, through iTunes and over-the-air updates.
iOS 6.1.6 is the final release supported for the iPhone 3GS and iPod Touch (4th generation).
iPhone OS 7
Main article: iOS 7 Apple announced iOS 7 on June 10, 2013 at its annual Apple Worldwide Developers Conference (WWDC) event, with release announced for sometime in Fall (Northern Hemisphere) or Spring (Southern Hemisphere) 2013. At their iPhone event on September 10, 2013, Apple announced the full release of iOS 7 for September 18, 2013, while also unveiling two new iPhone models: the iPhone 5C and iPhone 5S. With this release, support was again dropped for older devices, specifically the iPhone 3GS (due to hardware limitations) and the iPod Touch (4th generation) (due to performance issues). Supported devices on this release include the iPhone 4 onwards, iPod Touch (5th generation), the iPad 2 onwards, and the iPad Mini (1st generation) onwards. iOS 7.1.2 is the final release on the iPhone 4. But, Apple can detect an unauthorised install and deactivate the device.
iPhone OS 8
Main article: iOS 8 Apple announced iOS 8 on June 2, 2014 at its annual Apple Worldwide Developers Conference (WWDC) event, with release announced for sometime in Fall (Northern Hemisphere) or Spring (Southern Hemisphere) 2014. At their iPhone event on September 9, 2014, Apple announced the full release of iOS 8 for September 17, 2014, while also unveiling the iPhone 6 and iPhone 6 Plus. With this release, Apple resumed the cycle of dropping support for older devices, specifically the iPhone 4. Supported devices on this release include the iPhone 4S onwards, iPod Touch (5th generation) onwards, the iPad 2 onwards, and the iPad Mini (1st generation) onwards. iOS 8 has limited support on the iPad 2, iPhone 4S, and the iPod Touch (5th generation). iOS 8 was also the first version of iOS to have public beta testing be available, not just to developers. The first ever public beta was iOS 8.3 Public Beta 1. All major updates from this one on will receive public beta releases; minor ones don't usually receive them. The final version of iOS 8 is iOS 8.4.1. This release fixed some bugs present with Apple Music and patched TaiG Jailbreak.
iPhone OS 9
Main article: iOS 9 Apple announced iOS 9 on June 8, 2015 at its annual Apple Worldwide Developers Conference (WWDC) event, with public release on September 16, 2015. With this release, Apple did not drop support for any iOS devices, with all devices supporting iOS 8 being eligible for an upgrade. Supported devices on this release include the iPhone 4S onwards, iPod Touch (5th generation) onwards, the iPad 2 onwards, and the iPad Mini (1st generation) onwards, making iOS 9 have the most supported devices out of any other iOS release, with 22 devices. The iPad 2 is also the first iOS device to support six major releases of iOS, supporting iOS 4 to 9. This is the greatest amount of major iOS releases a single iOS device has supported, surpassing the iPhone 4S which supports five major releases (iOS 5 to 9), and iPod Touch (5th generation) supporting four major releases (iOS 6 to 9). However, iOS 9 has limited support on all 32-bit devices (iPhone 4S, iPhone 5, iPhone 5c, iPad 2, iPad 3rd generation, iPad 4th generation, iPad Mini, and iPod touch 5th generation).
iPhone OS 10
Apple announced iOS 10 on June 13, 2016, at its annual Apple Worldwide Developers Conference (WWDC) event, with a public release on September 13, 2016. With this release, Apple resumed the cycle of dropping support for older devices, specifically devices using either an A5 or A5X processor: the iPhone 4S, iPad 2, iPad (3rd generation), iPad Mini (1st generation) and iPod Touch (5th generation). iOS 10 has limited support on the iPhone 5, iPhone 5C, and iPad (4th generation).