Over the last couple of years, iOS has rightfully come under criticism for being less than rock-solid stable. This year's version appears to be aimed at offering better performance, increased stability and a more predictive user experience in which the operating system tries to anticipate user needs.
In addition, iOS 9 is packed with refinements and new features that try to anticipate and volunteer useful information to users based on what they're doing, along with under-the-hood optimizations that should give iPhone users additional battery life. iPad users, especially those with newer iPads, should consider iOS 9 a must-have update, as it unlocks multitasking features that power users have wanted.
iOS 9 is the third version of iOS to feature 64-bit code; it supports Apple devices dating back to the iPhone 4S, all versions of the iPad mini and all iPads since the iPad 2. It also runs on the fifth and sixth generation iPod Touch.
As always, before installing this update, go to Settings / iCloud / Storage & Backup and tap Backup Now. Or plug the device into your computer and click Back Up in iTunes. Be patient and wait for the backup to complete because you will want a full backup of your data in case something goes awry with the update. I didn't run into any problems updating my iPhone or iPads, but the old adage still holds true: Better safe than sorry.
Once the backup is done, update your iPhone by navigating to Settings / General / Software Update. For this, you will need a Wi-Fi connection and at least 50% battery life, or else the device will have to be plugged in.
Last year's rollout required over 4.5GB of available storage for the update to work. That resulted in many unhappy users who couldn't update wirelessly, especially those running devices with only 16GB of storage. This year, iOS 9 can be installed via Wi-Fi as long as there is at least 1.3GB of space, a far more reasonable requirement. Apple applied a few tricks to make this happen, including streaming updates that don't need additional space to be unpacked and only downloading those assets necessary for the device that is being updated.
If more room is needed, Apple crafted a workaround called automatic app deletions that temporarily deletes larger apps while preserving user-specific data. After the update is complete, any deleted app is automatically restored. There's also a new option to put off the update until a time when the iPhone is idle.
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