iOS 9 Allows App Developers To Require Devices With 64-Bit CPUs
It's been revealed that with iOS 9, Apple has given developers the choice of limiting their app to run on iPhones and iPads with 64-bit CPUs. While iOS 9 itself is capable of running on a large number of Apple's older devices, developers now have the ability of specifying that previous generations of hardware cannot run their apps. The reason is not to be mean or make owners of said devices angry, but rather to ensure devices will be compatible with the app being offered, and that they don't run the software poorly.
Should a developer decide to exclude all iOS devices that don't feature 64-bit architecture, that would mean all models of the iPod Touch, iPhones from before the 5S, and iPads before the first Air model wouldn't be able to install their specific app. If someone using on one of those older devices is browsing the App Store, apps with 64-bit CPU requirements simply won't appear for them, meaning they don't need to worry about looking for indications if an app can be installed and run properly.
Apple's first iOS device to feature 64-bit architecture was the iPhone 5S in 2013, with its A7 chip. But one of the greatest difficulties for developers has been the requirement that nearly all older hardware be supported. Chips like the A5 and A4 (in the iPhone 4S and 4, respectively) are pretty outdated and slow compared to today's standards, so giving developers the choice of excluding older devices is likely meant to make their lives easier and simplify app development.
This might be upsetting to certain iPhone and iPad users, especially if their device can run iOS 9, but it's more than likely that this limitation will mostly be applied to high-performance games that demand a lot from system resources. Someone with an iPhone 5 or 4S wouldn't have a great time trying to play that great new online battle game if it runs choppy or sluggish, so it might be better to limit them from buying it in the first place.
SOURCE 9 to 5 Mac