iOS 9 will be freely available for all devices which are compatible with iOS 8, and you can upgrade even if you’re still running iOS 7 on those devices. You can read more about iOS UK release date and exactly which iPhones and iPads can run it. See also: How to downgrade from iOS 9 to iOS 8.
While there were precious few reasons to compel anyone to upgrade from iOS 7 to iOS 8, things are different in 2015, and there’s a bunch of new features in iOS 9 which should prove tempting. This is even truer if you own an iPad, as you'll get multitasking features including picture-in-picture (for watching video while browsing the web, for example) and - on the iPad Air 2 - the ability to run two apps on screen at the same time. Other iPads get Slide Over where you can drag an app over one that's running to quickly check your calendar or reply to a message.
Below we've used two iPhone 5s, one running iOS 8.3 and another identical one running iOS 9.0 so you can see the changes and new features you'll get for free in iOS 9. In each case, iOS 8 is on the left, and iOS 9 on the right.
See also: How to get iOS 9.
iOS 8 vs iOS 9: home screen
Aside from new wallpaper, the home screen looks remarkably similar. You'll notice that Passbook is now called Wallet in iOS 9, Newsstand is gone (to be replaced by Apple News - this will appear in iOS 9.1, currently available via the Public Beta) and there's a new iCloud Drive app (more on that in a bit).
iOS 8 vs iOS 9: Recent apps
Because of the new 'proactive' Siri, recent or favourite contacts are no longer displayed when you double-tap the home button in iOS 9. Running apps are shown overlaid (much more like Android Lollipop) but you still swipe them off the screen to close them.
iOS 8 vs iOS 9: Siri and proactive
A minor change: Siri's interface has been updated to match how it looks on the Apple Watch. The animation for dictation has also changed and there's a vibration instead of a 'ding' when you hold the Home button or say Hey Siri.
A new feature in iOS 9 is that you can swipe right on the main home screen to see a Google Now-style screen with a search bar, news, plus suggested contacts and apps. You can still swipe down on any home screen to get the Spotlight search, and it's slightly redesigned as you can see above. Spotlight now offers up nearby places, Wikipedia entries and news in searches, as well as the usual matching apps, and results from emails, contacts, notes, messages and more.
Proactive will also display suggested apps based on time, so if you always check the weather and news when you wake up, these apps will be shown in the list. Music will be shown on the lock screen if you listen at certain times, too.
iOS 8 vs iOS 9: Search for settings
Finally, you can swipe down in Settings to search. This is way quicker than trying to remember which sub folder a particular control is in. There's a new menu for Battery now, too. You can check which apps are using most power, as well as manually enabling a power-saving mode. The Low Power mode automatically kicks in when the battery gets down to 20 percent, and disables when it charges above 80 percent full.
iOS 8 vs iOS 9: Notes
Notes has had a lot of attention lavished upon it. Apple says most people use Notes and has therefore added lots of new features. You can now format text, add headings, bullet lists and checklists. The sketching tool is handy (more so on a big iPad screen, admittedly) but the ability to paste in links from other apps via the sharing mechanism is very useful. Above you can see a link from Safari, but you can also take photos or add them from your camera roll.
iOS 8 vs iOS 9: Sharing
As just mentioned, you can now Share to Notes from the activity list when you tap the Share button in an app such as Safari. The screen has been changed slightly, too, with a bigger Cancel button and a bigger radius on all rounded corners (a change noticeable throughout iOS 9).
Not all sharing screens look different, however. When in the Photos app, below, it looks pretty much the same as before.
iOS 8 vs iOS 9: Photos
Speaking of the Photos app, you'll notice in the iOS 9 screen above, right, that there's now the option to Hide photos. When a photo is 'hidden' it's removed from Moments, Collections and Years, but will still be visible in Albums.
A nice new feature in Photos is a scrubber bar at the bottom. You can swipe along this to quickly scan through your camera roll or in any other view.
iOS 8 vs iOS 9: Camera app
There are a couple of small changes to the camera app. In iOS 9 there's no Auto, On or Off label next to the flash, but merely a slash through it if it's disabled. The same goes for HDR which has been swapped with the timer for some reason.
iOS 8 vs iOS 9: iCloud Drive
At last, there's an app for iCloud Drive. Below, you can see two screens from iOS 9. The first is the prompt you get when you sign into iCloud with your Apple ID. The second is an iCloud Drive sub folder. You can see all your files stored in iCloud and open them where possible with apps on your iPhone or iPad.
iOS 8 vs iOS 9: Reading view in Safari
In iOS 8, you could change the size of the font in reading view. But in iOS 9 you can change the font from the default - the new San Francisco font which is used throughout iOS 9 - and the colour of the background.
iOS 8 vs iOS 9: Reminders
The changes are more subtle in the Reminders app. They're useful, though. For each list you can now see a summary of how many items are overdue, and there's a new list called Scheduled which offers a summary of all the reminders which are overdue, or due today.
iOS 8 vs iOS 9: Passbook vs Wallet
There's little more than a name change from Passbook to Wallet in iOS 9. The comparison below exaggerates the changes because we've added a card to Apple Pay which arrived in the UK in July on an iPhone 6 - the iPhone 5 isn't compatible with Apple Pay because it doesn't have NFC. Even if you don't have a compatible iPhone, though, you'll be able to keep coupons, vouchers, tickets, loyalty cards and more in one place.
New iPad features in iOS 9
When you swipe in from the right-hand bezel, you'll get a list of running apps which you can snap to a column view as shown above. The app already running full screen dims down and becomes unresponsive until you swipe the column out of the way.
The iPad Air 2 - and perhaps any new iPads launched in 2015 - lets you run two apps simultaneously. You can adjust the space given to each by dragging the central bar between them, just like on a Windows 8 device.
Picture in Picture
When you're watching a video or using FaceTime, tap the Home button in iOS 9 to make the video shrink to a thumbnail. You can then tap to open another app and the video will keep playing. You can then move it around and resize it to your liking.
It's not clear yet whether only the native Videos app will support Picture in Picture or whether other apps such as YouTube will support it. Let's hope so.
Yet another great new feature for iPad owners is the new text selection method. When you put two fingers on the screen over the keyboard the letters disappear and you can move the cursor around and more easily select text.
Plus, the keyboard gains extra controls as seen in the top row above: cut, copy, paste, plus bold, italic and underline.
See also: 12 other new features in iOS 9