Apple updated the App Store support page of its developer website ahead of the official release of iOS 9 on Sept. 16, revealing that the outgoing iOS 8 has an adoption rate of 87 percent among all compatible devices with the mobile operating system.

Only 11 percent of compatible devices are still running iOS 7, with earlier versions of Apple's iOS accounting for only 2 percent.

According to Apple, the data was sourced through user visits made on the Apple Store on Sept. 14.

In comparison to where the iOS 7 stood at the same time last year, when it was about to be replaced by then incoming iOS 8, the adoption for the outgoing mobile operating system is lower by three percentage points. The uptake of iOS 8 is only moderate despite booming sales for iPhones and the launch of Apple Music with the update to iOS 8.4.

In comparison, the latest version of rival Google's Android mobile operating system, Android 5.1 Lollipop, only has a 5.1 percent adoption rate. The extremely low figure is due to the fact that Android updates take much longer to be adopted by users, partly due to carriers and smartphone manufacturers needing to tweak their interfaces and apps to be compatible with new Android versions.

Mixpanel, mobile analytics company, said that iOS 9 already holds a 1.04 percent adoption rate even before its official release, with the operating system installed in developers and beta testers. The number is expected to rise significantly upon the upcoming release of Apple's newest operating system.

Apple previously revealed that the iOS 9 will feature several improvements and updates that would make the mobile experience much better for users, including lower memory requirements and faster speed.

All devices capable of running iOS 8 will be able to upgrade their operating system to iOS 9. Users that do so will see significant upgrades in built-in apps such as Maps, News and Notes, along with improvements to app multitasking and Apple Pay.

The new iOS 9 will be taking advantage of the 3D Touch feature of the upcoming iPhone 6S and iPhone 6S Plus, in addition to Apple Pencil and Smart Keyboard support for the iPad Pro.