It seems like every time a major software revision comes along, it’s described as the “biggest ever.” In the case of iOS 5, though, that might not be hyperbole—there’s hardly a part of Apple’s mobile operating system that isn’t altered in some way by the latest update.

Don’t think that this is just change for change’s sake, however. By and large, iOS 5’s changes are for the better, spackling a number of shortcomings and gaps in functionality that have existed since day one.

Tempting as it may be to dub iOS 5 the “Snow Leopard” of iOS, though, it’s clear there’s a lot more to this than simply filling gaps. iOS 5 marks the first major revision of iOS to be simultaneously released for the iPhone, iPod touch, and iPad. It also finally brings feature parity between the CDMA (Verizon) and GSM (AT&T) versions of the iPhone. In fact, all of Apple’s iOS devices are on the same page now (with the exception of the few specific features—such as Siri voice-control—that are limited to the iPhone 4S).

And that page isn’t exactly what you think it is, either. With iOS 5, Apple’s theory of the post-PC era finally moves into practice. No longer are iOS devices second-class citizens, tethered to the sinking anchor of a personal computer. With iOS 5, it’s possible, for the first time, to use your iPhone, iPod touch, or iPad as your one and only device.

PC Free, with every purchase

Despite touting the PC-free capability on its list of features at this year’s Worldwide Developers Conference, the ability to use your iOS device sans PC isn’t really one feature, but a collection of them. That said, it represents perhaps the most important shift ever in thinking about Apple’s non-PC devices.

Going back to the original iPod, Apple’s non-PC devices have been viewed as accessories. You bought an iPod to go with your computer. Your iPhone synced data with your computer. Your Apple TV streamed content from your computer. By the time Apple released the iPad, that concept was straining at the seams. After all, what is the iPad if not a computing device in its own right? Why does it need to be subservient to a Mac or PC?

As of iOS 5, your iPhone, iPod touch, or iPad can stand in the place where it lives, with no need for a Mac or PC to prop it up. The importance of this change is impossible to ignore. A year and a half ago, I argued that the iPad heralded a third revolution, but where that was a warning shot—a promise of things to come—iOS 5 finally delivers on that promise.

Setup man: The setup of a new device is perhaps where the distinction is most apparent. Whereas previous iOS devices would welcome you with the all-too-familiar instruction to plug them into a computer running iTunes, iOS devices now display a friendly welcome message—much like when you set up a new Mac.

If you’re starting with a fresh device, iOS 5 will walk you through a series of steps to get it set up. You’ll be asked if you want to enable location services, prompted to choose a Wi-Fi network, then given the option to restore from an iCloud or iTunes backup or to set up a brand new phone (or iPad, or what have you). If you set it up as a new device, you’ll be asked to enter your Apple ID (or create a new one), then given the Terms and Conditions for iOS, iCloud, and Game Center, as well as Apple’s Privacy Policy; if you agree to those, you have the option to activate iCloud, iCloud Backup, and Find My iPhone. As a last step, you’re given the option to allow the device to send diagnostics and usage data back to Apple—you can also opt out or, if you do choose to enable it, turn the feature off later under Settings -> General -> About -> Diagnostics & Usage. This information can help Apple improve its products, but the company also warns that it may include some location data.

It’s a pretty straightforward process, and one that even a technological neophyte shouldn’t have too much trouble with. Apple provides help links for most screens, explaining what a given technology is and why a person might want to use it. Much kudos in particular to the company for making Find My iPhone a part of every iOS device setup process. Having known a number of people who have lost their devices, or had them pilfered by nefarious wrongdoers, this is a feature that can genuinely help people—if they set it up. And now, thanks to iCloud, it’s available to all iOS device users for free.

Mind the Gap: Apple has also taken this opportunity to fill in numerous gaps in functionality that used to send one scurrying for their computer. For example, you can now add photo albums on the iPhone. You can create playlists. You can delete songs from your Music library (though, woe still betide you if you want to add anything to that library without going through Apple’s prescribed methods). And, joy of joys, you can now update an iOS device’s software right from the device itself, over the air—a capability that has been deployed by many of Apple’s competitors in a decidedly hit-or-miss fashion.

Other places where Apple is shucking the bonds of the PC include backups. In the past, iOS devices have backed themselves up while syncing with iTunes—and while you can still opt to keep things that way, either via cable or the new Wi-Fi Syncing (see below), those who choose to eschew a computer can back up their devices online, via iCloud.

To reduce the amount of space needed—each iCloud account comes with a free 5GB, and the smallest iOS device Apple sells is 8GB—only your data is backed up. And not even all of your data: Any media you’ve downloaded from the iTunes Store doesn’t count against your total, and that includes apps as well as music, video, and books. You can also selectively choose which apps’ information you want to back up in Settings -> iCloud -> Storage & Backup -> Manage Storage (or Settings -> General -> Usage -> Manage Storage).

Like Wi-Fi Syncing, backups happen when your device is on a Wi-Fi network and plugged in, so if you let your iPhone or iPad charge over night, it should be all set when you pick it up in the morning.

You can also manage your device’s internal storage. Settings -> General -> Usage provides a list of all installed apps—although many of the apps that ship on the phone are not present—and their size; tap on any to see the size of any documents or data that are being stored in that app. (Often, those file sizes are far smaller than the app itself.) There’s a Delete App option available on most of the screens as well.

iOS software updates are another task that used to require running to a computer; now that’s built in as well. It’s available under Settings -> General -> Software Update though, as you might expect, we’ve been unable to test it in the final version of the software so far.

Finally, should you decide the name of your iOS device isn’t quite cutting it, you don’t have to turn to a computer to change it. Just navigate to Settings -> General -> About and tap on the Name field to enter a new one.

Notify this

By now, the pattern in Apple’s major iOS updates ought to be pretty clear. Every significant version change has brought at least one very important systemwide update that addresses a shortcoming, along with a handful of feature enhancements and other tweaks. In version 2.0, that was the App Store; in 3.0, it was cut, copy, and paste functionality; in iOS 4, we finally got multitasking. In iOS 5, that role is played by improved notifications.

It wasn’t long after push notifications were finally introduced in iOS 3 that frustrations began popping up right alongside them. The blue alert dialog that appears to let you know you’ve got a new text message or update you on your sports scores is handy and all, but it can induce plenty of annoyance when you’re in the middle of doing something else. Plus, if you dismiss the notification just to get it out of the way, there’s no way to get back to it later.

iOS 5 improves notifications in three key ways: the introduction of banner notifications, the addition of Notification Center, and improvements to lock-screen notifications.

Banner notifications solve the problem of having notifications interrupt everything you’re doing. Instead of appearing as a dialog box, the top of the screen flips down—like one of those rotating billboards—to reveal a small icon from the notifying app and a message. Tapping on the banner takes you to the app in question; but if you don’t tap the notification, it will linger for a few seconds and then disappear again.

But what if you don’t quite tap fast enough? No worries—that’s where Notification Center comes in. Just swipe down from the menu bar and you’ll drag down a sheet containing all of your recent notifications, arranged by the originating app. As with the banner notifications, tapping anything in Notification Center will take you to that app (and usually to the relevant item).

You can clear all the notifications for any app by tapping the ‘x’ icon opposite its name, then tapping the Clear button that appears. However, there’s no way to clear just a single notification without tapping on it—my experience with iOS’s multitouch conventions tells me I should be able to swipe across a notification and have a Delete button appear, but sadly that doesn’t appear to be the case; it’s an all-or-nothing proposition.

Notification Center gives you two choices for organizing the order in which apps appear in it: manually or by time. If you choose by time, the app with the most recent notification will show up at the top, followed by the app with the second most recent, and so on. If you opt for manual organization, then the apps will appear in the same order that they do in Settings -> Notifications. You can reorder them there by tapping the Edit button and dragging them into your desired sequence.

In addition to notifications, Notification Center on the iPhone includes two special entries: a Weather widget and a Stocks widget. The Weather widget displays the current conditions and temperatures for the first location in the iPhone’s Weather app (if you enable the Weather app’s new Local Weather option, that’s what will show up in Notification Center). Tap on the widget and you’ll be taken to the Weather app.

The Stocks widget shows a scrolling ticker of any symbols you’ve added in the Stocks app, along with their current quote, whether they’ve gone up or down, and—for companies—their current market capitalization. You can tap and drag on the scrolling stocks, just in case the one you wanted to look at scrolled by too fast. And tapping on the widget will take you to the Stocks app.

Like the other apps in Notification Center, you can place the widgets wherever you like, if you’ve chosen to organize them manually. (If you organize by time, they’ll always be at the top.) However, you can’t configure anything else about them, other than turning them off or on.

While I turned the Stocks widget off—I don’t need constant reminders of our economic woes—I find the Weather widget extremely handy. I hope that Apple will extend this widget space to further apps and perhaps even third-party developers at some point in the future; I can imagine plenty of apps where I’d want the option to get a quick glance at their status without launching them—a news reader for example, or social networking client, or an app that provides sport scores. Or, for that matter, let third-party makers of weather and stocks apps provide their own widgets, if users would prefer them.

The last part of the notifications overhaul in iOS 5 is the improvement to the lock screen. In previous versions of iOS, if you got multiple notifications while your phone was asleep, they would appear in a blue dialog box along with a brief description: two missed calls, a voicemail, a text, etc. But once you unlocked the phone, those messages would disappear, so it was incumbent on you to remember what they were.

Now, your lock screen gives you a scrollable list of all your notifications, listed in the order that you received them. As with Notification Center and banners, an icon tells you what app the notification is for, along with a short description of the alert. Swiping any icon will unlock the phone and take you right to that application.