IOS 9

iOS 9 is the ninth release of the iOS mobile operating system designed by Apple Inc. as the successor to iOS 8. It was announced at the company's Worldwide Developers Conference 2015 on June 8, 2015 and was released on September 16, 2015. iOS 9 focuses less on new features and more on under-the-hood optimizations, as well as battery improvements. iOS 9 only requires over 1 GB or iPhone or iPad space to download.

History
OS 9 debuted at the  Apple Worldwide Developers Conference on June 8, 2015, with iOS 9.0 beta 1 being made available to registered developers straight after the keynote, and a public beta made available to members of Apple's  Beta Software Program in July. iOS 9 was released publicly on September 16, 2015.

iPhone

 * iPhone 4S
 * iPhone 5
 * iPhone 5C
 * iPhone 5S
 * iPhone 6
 * iPhone 6 Plus
 * iPhone 6s
 * iPhone 6s Plus

iPad

 * iPad 2
 * iPad_(3rd_Generation)
 * iPad_(4th_generation)
 * iPad Air,
 * iPad Air 2
 * iPad Pro

iPad Mini

 * iPad Mini
 * iPad Mini 2
 * iPad Mini 3
 * iPad Mini 4

iPod

 * iPod Touch (5th generation)
 * iPod Touch (6th generation)