Apple's iOS 8 took several gigabytes of free storage space in order to download and install onto our iPhones or iPads last year. For 16GB (or, dare it be said, 8GB) iOS device owners, this was a problem only made worse by the prevalence of big, heavy apps on the App Store.
Rather than its 4+GB file size, the over-the-air (OTA) software update for iOS 9 is set to weigh in at just over one gigabyte. Better yet, a developer feature called “App Thinning” should make it possible for iOS developers to reduce the size of their applications, too. In a recent article, Ars Technica explained how App Thinning works – the feature is actually made up of three defined, separate elements.
The first is “App Slicing.” This allows iOS developers to ship apps which only install the code your particular device needs. This might be “3x” assets and 64-bit support for the iPhone 6 Plus, but, on the other hand, it could be “2x” 32-bit code for an iPhone 5s. At the minute, applications include all the code any iOS device could possibly need. With App Slicing in iOS 9, users will indeed be able to have iOS apps only install the required code, meaning they'll take up less space on your iPhone or iPad.
Ars Technica continues:
The second feature is a bit more complicated. On-Demand Resources (ODRs) are chunks of apps that are only downloaded when they're needed and are cleared from your device when you're done with them. Apple has lots of details about the implementation of ODRs on its developer site, but the basic pitch is that you don't need to be using all the assets in your app at any one time.
For example, in a game with multiple levels, Apple suggests that your app only really needs to have the data for the level you're on and the levels immediately following it, not necessarily levels you've already beaten. For an app with a tutorial, it might download the assets for that tutorial the first time you use it but delete them from your device after it's clear that you're not going to need the tutorial again. An app with in-app purchases could decline to download those assets until you actually make the purchases.
Images and media files can be tagged as On-Demand Resources, but not executable code, according to the publication. Nevertheless, this should also have a positive impact on the size of installed apps on your iOS 9-powered device.
Finally, a feature called “Bitcode” allows an iOS device to compile binaries needed for that particular model, in a similar way to its aforementioned App Slicing functionality. Ars Technica adds: “Since Apple is compiling the app on-demand, it also implements any compiler improvements that Apple makes without requiring a developer to resubmit their applications.”
All of this means owning an 8GB iPhone 5c, for instance, isn't going to be as troublesome under iOS 9.