iOS 4, previously known as iPhone OS 4, is a major update to Apple's mobile OS which brings a handful of significant changes—namely Apple's implementation of "multitasking" plus the opening up of thousands of APIs to third-party developers—while the rest of the improvements are basically tweaks to existing functionality.

We'll say up front that we like the update. For iPhone 4, iPhone 3GS, and iPhone 3G users (as well as second- and third-generation iPod touch users), iOS 4 will add useful functionality that will make your device more useable than ever. There are, however, some obvious downsides, and we'll address those in this review.

Because iOS 4 is launching ahead of the new iPhone 4 (and it runs on more devices than just the new iPhone), we're reviewing it separately from the phone itself. There is some functionality that is specific to the iPhone 4, which we'll address in that review when it comes out. For the purposes of this review, though, we used iOS 4 on an iPhone 3GS—the most current iPhone available ahead of the iPhone 4 launch.

Multitasking

The biggest and most obvious update to iOS 4 is the ability for third-party applications to "multitask"—that is, you don't have to terminate them in order to do something else in another app. This is functionality that has been requested of Apple since the launch of the original iPhone in 2007, and it has been a long time coming. (Only the iPhone 4, iPhone 3GS, and third-gen iPod touch get multitasking.)

Apple's own apps have always been able to truly multitask (you can get iCal alerts while playing a game, for example, or listen to music from the iPod app while reading a webpage), but third parties can now take advantage of alimited set of multitasking capabilities in order to make things easier on the user.

Why "limited"? Because iOS multitasking isn't really multitasking in the traditional sense—it's certainly not what you get on a desktop computer, or even what you get from Apple's own iPhone apps. Apple claims that it only allows for certain functionality so that the OS can continue to preserve battery life and performance in a sane manner. So, what exactlycan you do with this new feature? Really, the answer isn't so much that apps will be "multitasking," but rather that they'll be "doing a few things in the background":

• Audio: you can now listen to streaming music from apps, like Pandora or newscasts through the NPR app, while doing other activities on your phone. Previously, you would have to quit out of the app (and therefore stop your music stream) if you wanted to respond to an SMS or read your e-mail, and now that's no longer the case. Hallelujah.
• VoIP: similarly, you can carry on Voice Over IP calls on services like Skype without having to quit the app if you need to perform other tasks.
• Location: apps that need to poll your location, such as GPS and direction apps, will be able to do so in the background. No longer will you need to keep the app in the foreground just so it can keep track of where you are.
• Local notifications: third-party apps no longer have to rely solely on push notifications if they want to alert you of something on your phone. If you have an alert set in, say, one of Omni's applications, it can ping you when the time comes instead of having to go through a convoluted series of Internet tubes to get to you. This, of course, reduces your reliance on an Internet connection to get certain types of alerts and helps cut down on overall wireless bandwidth.
• Complete tasks: if you start a task in an application and then switch to another one (such as downloading a new map in your favorite game), it can now complete the task in the background instead of forcing you to sit there and wait on it.
• Fast app switching: this is basically "pausing" an app where it is, which allows you to quickly switch away from it and then switch back, picking up where you left off.

Whatcan't your third-party apps do while in the background?

• Grab new updates: those of you who were hoping that your Twitter, IM, or IRC client would pull down updates while hanging out in the background will be disappointed. Unless those apps make use of push notifications to alert you of new messages (as the AIM app does), apps won't be able to check for updates on their own unless they're in the foreground.
• Work across the entire OS: users have long hoped that some of their favorite apps (such as TextExpander) would be able to work in all parts of the OS, such as Mail and Messages, but that won't be the case. This isn't Mac OS X here—Apple still wants to keep each app to itself for the most part.

Now that we've told you what the new feature can and can't do, we'll tell you how to use it. Anytime you launch an app and then switch to another app, the first app is automatically "backgrounded" and added to your app drawer. You can access this drawer from anywhere by hitting the Home button twice, which will slide your screen up and show you a row of icons that you can swipe through.

If you swipe right immediately after hitting the Home button twice, you'll always get the orientation lock (more on this later) as well as your audio controls for the app that's currently playing audio. If you swipe right, you'll just keep getting apps that you recently used—tap any of the app icons to switch back to that app, and it will pick up exactly where you were before you switched away. Although the multitasking feature is limited overall, the ability for the OS to keep your spot in whatever you were doing is certainly welcome. (It's worth noting that many developers have put in good effort to save your state within their apps in order to replicate this on their own.)

One odd thing we noticed about the app drawer is that it seems to stay in portrait mode when you double tap the Home button while in landscape:

The drawer itself coming up on the side (instead of the bottom) isn't so much the problem, but the app icons are still rotated as if the phone were in portrait. Someone couldn't at least rotate the icons so they're facing the right way when viewing it in landscape? This seems like an oversight that is atypical of Apple's usual attention to detail.

And, although Steve Jobs trashed the idea that users should be managing apps on their own (he said something along the lines of "If you have a task manager, you have failed!" at a media event in April), you can quit the currently running apps if you want to. You shouldn'thave to—Apple basically freezes all their processes in the background unless they're performing one of the aforementioned kosher functions, so they shouldn't be sucking up any of your performance—but it makes those of us with neatness neuroses happy.

Just tap and hold on the app that you want to close in the app drawer, and they'll all begin to wiggle (just like if you were to tap-and-hold on the home screen to move an app around). Tap the minus sign in the upper left-hand corner and the app will disappear.

Given all of these considerations, Apple's implementation of "multitasking" works largely as expected (aside from the odd icon rotation in landscape mode). One downside is that you can no longer program the double-clicking of the Home button to do anything else—this functionality is now reserved solely to access the app drawer. That said, it eventually becomes second nature, and the benefits generally outweigh the losses. Audio controls still come up when you double tap the home button while the device is locked.

Compared to other smartphones, Apple's implementation is (unsurprisingly) the most limited. For example, Windows Mobile 6.x allows all apps to do whatever they want in the background—there's no differentiation between first- and third-party either. (Comparatively, Windows 7 Mobile has background state-saving for third-party apps, but no background multitasking.) Palm's (now HP's) webOS is similar to Windows Mobile 6.x: no restrictions on what apps can do while not in the foreground. Android's model is a bit more mixed, but services can run in the background unless the OS decides to terminate them (due to lack of memory, battery running low, etc.).

Developer Marco Arment hasdescribed what he thinks would be a happy medium in iOS 4 that would give users (and developers) more of what they want without too many sacrifices. Basically, the application would be able to tell the OS how often it wants to send a request for new data, and the OS would be left to decide whether it wants to execute depending on various factors like battery level or CPU usage. This would indeed allow for more flexibility in iOS 4 backgrounding, and we can only hope that Apple takes some of Arment's advice for future OS updates.

Home screen and overall UI updates

After multitasking, the second major category of changes that comes with iOS 4 is the overall tweaks to how the home screen works.

Folders

The most notable of these updates is the addition of folders: users can finally group their apps based on genre, taste, or any other random combination they can think of. You can do this by dragging one app on top of another:

iOS 4 will prompt you to name the folder, and the default will be whatever genre the OS thinks makes the most sense. You can name it whatever you'd like, though, and you can edit the name later by pressing and holding on the icon on the home screen and then tapping on the folder when it starts to wiggle.

You can store up to 12 items in a folder, which I find to be plenty—there aren't many genres of apps where I have more than 12 items. The only place I can see this limitation being a serious problem is for heavy iPhone gamers: in this case, you might need to subcategorize your games into different types of games (perhaps strategy games versus shooters, for example). There's currently no way to nest folders within folders, which is fine with me, but perhaps more neurotic organizers will want deeper nesting.

One little detail I like about folders is the way that it handles number badges. Any app within a folder that displays a number badge—say, unread items in Mail or games to play inWords with Friends—will also have its badge displayed on the folder icon.

Overall, the implementation of folders is good, though I've made a few observations about my own behavior while using them. For one, it's pretty easy to forget where you've stored your apps after you've organized them all into folders (at least in the beginning). It's not very good for people who have a visual memory: most folder icons look the same (and you can't set an icon for a folder), so if you're looking for a specific icon that happens to be buried somewhere, things can get frustrating. I have found myself continually swiping around on the phone for a specific app I'm looking for, eventually giving up and going over to iOS 4's built-in Spotlight search to just make the phone find it for me. In fact, I never really used the iPhone's Spotlight search for any regular reason until now—it seems to have turned into my personal "find my app" search thanks to folders.

One thing about folders that annoys me, though, is their behavior after you've launched an app. The folder doesn't close on the home screen once you've decided to go into an app within that folder: it stays open so that when you hit the home button again, you're returned to that specific folder and not just the home screen. I regularly found myself irritated by this, as I expect to go back to the home screen when I hit the home button. But with iOS 4, I now have to perform an extra button-press to get to where I want to go. Several other iOS 4 users seemed to agree with me when I discussed this with them, though a few said they liked the behavior. Your mileage may vary.

The home button now does more—and less

Tapping on the home button once will either take you back to your real home screen or the last folder you were in. However, tapping ittwice will bring up your multitasking app drawer, as we discussed earlier in the multitasking section. Here, you can quickly flick through to find recently used apps. If you swipe to the right (so that you're moving left) after double tapping the home button, you willalways get the audio controls for whatever audio you're listening to at the time (default is iPod app) as well as the screen orientation lock.

Let's all turn towards Cupertino and give a moment of silence in appreciation of the software screen orientation lock.

Long requested by bed iPhoners, drunk iPhoners, and pretty much anyone who doesn't always use their iPhone while in a standard bodily position, Apple has finally given us a way to lock the screen's orientation across the entire device. So what if it isn't a hard slider like the one on the iPad—that might be ideal, but I'll take what I can get. When you lock the screen, the iPhone will show you a little lock icon in the upper right-hand side of the menubar.

Strangely, the orientation lock only seems to be able to lock the screen into portrait mode. You can't lock a screen into landscape mode—in fact, if you try to invoke the orientation lock while you're already in landscape mode, the OS will switch back to portrait to lock. As a serial landscape hater, this doesn't bother me so much as it perplexes me, but landscape lovers will undoubtedly be frustrated by this.

The downside to this new magical ability added to the home button is that you can no longer assign that function to anything else. Previously, in iPhone OS 3.x, there was a setting where users could set the double tap to launch the camera (my personal favorite), Phone Favorites, iPod, or Search, and this has gone by the wayside. I'm disappointed that I'll no longer be able to launch the camera app as quickly as I would like, but the trade-off seems to be worth it. It'll just take some getting used to.

Change your home screen background

It's not a major functionality change, but Apple has added the ability to change your home screen background in addition to your lock screen background (which was the only thing you could change previously). When you're browsing through images in the Photos app, tap on the image you want and tap the icon in the lower left-hand corner with the arrow. Then choose "Use as Wallpaper," which will then present your options:

Be warned: just like on the desktop, crazy backgrounds can be distracting and draw more attention to the ever-so-slightly transparent menubar at the top. Additionally, this feature appears to be disabled for iPhone 3G and second-generation iPod touch users. Why? Nobody knows. Apparently you really need some hardcore processing power in order to display custom wallpapers. We're being snarky of course, but a reader offers up a probable explanation in the commentshere. 

Major updates to Mail

The core functionality of Mail has remainedlargely the same since iPhone OS 3, but Apple has made a number of changes to the interface. The most notable of these changes is the addition of a unified inbox, where you can now see all of your e-mails fromall of your inboxes in one giant dump. I can't say I've ever wanted this feature (I never use it on the desktop version of Mail), but it has been one of the most oft-requested additions to iPhone version of Mail, showing that the majority of iPhone users apparently have no desire to keep certain aspects of their life separate.

The above screen can be found by going back a couple of levels in Mail if you happen to be looking at a specific inbox. The difference between "Inboxes" and "Accounts" is that Inboxesonly shows you in the incoming mail for those respective accounts, while Accounts will show you everything from that account, including your folders, drafts, trash, and more.

A more useful addition to Mail is the arrival of threads. Now, you can have your messages grouped by thread so it's easy to go back and look at what was said in the past. An e-mail thread is indicated with a number in a gray box to the right of the message in your inbox:

The number obviously refers to the number of e-mails in that particular thread. When you tap on the message, it will take you to a screen with every e-mail in that thread. From there, you can read whichever e-mails you'd like. Some might find this irritating, as it requires at least one extra tap to get to the e-mail you want to read, but you can turn this setting on or off by going into Settings > Mail > Organize by thread.

The threading functionality extends to how you delete or archive messages as well. If you swipe right to delete a thread (like you would a normal message), Mail asks you if you want to delete all [x] messages from that thread. There's a nice touch here when it comes to handling different e-mail accounts: if you're using a Gmail account, for example, Mail will ask you if you want to archive that entire thread instead.

What's annoying, however, is that there's no easy way to delete a message from your Gmail account—it's like the olden days of Gmail when Google thought you might legitimately want to save every piece of spam you ever got. The roundabout way to delete a message from a Gmail account is to move that message to the Trash folder, but that requires several actions and is generally a pain to do. (Update: It appears there's a setting to change this. If you go into the settings for the Gmail account, you can turn the message archiving to "off.")

Finally, Apple has added the ability to open e-mail attachments in third-party apps. This is certainly a welcome feature, especially for those who would prefer to use a better piece of software from the App Store to manipulate photos or read PDFs.

(One last major update to Mail that we didn't get a chance to test was the ability to use multiple Exchange accounts. This is definitely ahugeimprovement for enterprise users who were annoyed at being tied to just one account under iPhone OS 3.x.)

Changes to the iPod app

As we mentioned in the section on the home screen changes, Apple has added audio controls to its app drawer that appear when you double-tap on the Home button and then swipe right. These audio controls not only work on the iPod app; they also work forany app that streams audio (Pandora, Last.fm, NPR,This American Life, to name a few). This is now the official way to access the iPod controls if you're not going to launch the app itself and if you're not looking at a locked iPhone screen.

Within the iPod app itself, barely anything has changed except for the ability to create and edit playlists. In fact, even this isn't very new: Apple has basically revamped what was previously known as "on-the-go playlists," which was an old concept anyway that was carried over from the days when iPods didn't have touchscreens. Now, under the (mostly just renamed) system, there's a menu item to "Add Playlist" toward the top of your playlist list:

When you tap it, the device will prompt you to enter a name (which you can edit later). Once you do this, you can then sift through your list of songs, artists, playlists, videos, podcasts, and more to put together a custom playlist. The list can be mixed in the type of media you add; skip around between videos, songs, and podcasts all you like.

If you want to rearrange items in the list, hit the "Edit" button and tap on the right-hand side of the item name where there's a little icon of a list and drag it. You can also delete items, add items, or clear the whole list. You can use this same functionality to edit playlists that you've created from the computer.

Changes to Camera and Photos

The additions made to the Camera app are comparatively minor, but they're worth noting nonetheless, and there are enough updates to get us to create a whole section in this review.

iPhone 3GS and 4 users can now tap to focus while recording video, just like they could previously with the still camera. Users can now also make use of the 5X digital zoom in the Camera app which, as one might expect, produces generally horrible results. But hey, who are we to argue? There's a reason why so many consumer-level cameras have digital zoom, and now the iPhone has it too.

When you e-mail photos from the Camera or Photos app, you can now choose from multiple sizes of a photo instead of letting the iPhone decide for you. This is useful if you know you need to cut down on bandwidth or data use, either on your end or the receiver's end:

My favorite part of the Camera app updates is the addition of faces and places. If you sync your iOS device with iPhoto on your computer (and, accordingly, if you use the Faces feature in iPhoto on the Mac), it will now give you the option to view photos by who's in them. Similarly, you can view photos based on where they were taken, and this feature isnot necessarily dependent upon iPhoto. iOS 4 can pull the geolocation data attached to your photos taken on the phone, as well as whatever data may come with images you have synced, and show them on a map:

For those who like to travel, this is a pretty neat feature that gives you easy access to photos taken in different locales. It's a crowd-pleaser too.

Bluetooth keyboard support

The iPhone has always had pretty sad Bluetooth support compared to pretty much everything else, but Apple has added wireless keyboard support to its short list of supported Bluetooth services.Just like on the iPad, you can now pair a keyboard—Apple or otherwise—with your iPhone if you absolutely need to produce mass amounts of text on your phone. Again, only iPhone 4, iPhone 3GS, and third-gen iPod touches get Bluetooth keyboard support.

You can pair your keyboard by going into the Settings app and then General > Bluetooth. You must first turn Bluetooth on, and then make sure your keyboard is discoverable. Once you pair the two, you can use the keyboard to enter text into any app that takes text entry, and you can perform a limited number of commands right from the keyboard (similar to the iPad):

Here's the text that I wrote in the Notes app with a Bluetooth keyboard paired with the iPhone, for those of you who would rather not read Marker Felt in a screenshot:

This is a new note that I'm writing with the Bluetooth keyboard. The standard keyboard commands work, such as command + A for select all, command C/X/P for copy/cut/paste, and so on. On the Apple wireless keyboard, the built-in sound buttons can control the iPhone's audio (play/pause, skip ahead or back, volume), and the keyboard's brightness controls can adjust the iPhone's brightness. What doesn't work: command + tab, more complex commands.

As we wrote in ouriPad review, keep in mind that this is not good for any kind of input that requires a pointer—you can't use a Bluetooth mouse with the iPhone, so you have to reach out and touch the device with your finger if you want to do something on the screen that you can't do with the keyboard. This feels somewhat unintuitive while you're using a standard computer keyboard (which seems to put our brains into "normal computer" mode), which is part of the reason why we don't think anyone will be using a regular keyboard with an iPhone very often. It's generally impractical, and how likely are you to have a keyboard in your bag while you're not at home? I can't see myself using this feature after writing this review, but it's is nice to have it there for emergency use.

Unfortunately, a swath of other Bluetooth services are still unavailable to iOS users, such as pairing with my favorite Mac app for interfacing with a Bluetooth-enabled phone,BluePhoneElite. At this point, I have given up hope that Apple would ever allow something like that, and you probably should too.

Odds and ends

There are tons of smaller changes in iOS 4 that are worth observing:

Character counts, subjects in Messages

There's now a character count for the Messages app so you can see how long your SMS/MMSs are. You can activate it by going into your Settings > Messages and sliding the character count slider to "on." After that, when you're typing a message to someone, the count will show up on the right-hand side above the "Send" button:

If you choose to turn it on, there are separate fields for "Subject" and for the rest of your message. The character count doesn't show up when you type into the subject—only the message part. The phone doesn't allow you to send a message with only a subject, though you can send a message without one. The difference appears to be that a message with a subject comes through as an MMS, while one without is an SMS. (We can see this being useful if you're sending a photo or video in the body, but otherwise, not so much.)

New/updated spell check

The spell checking feature in iOS 4 has been refined—no longer does the device simply change your word to the word it thinks it should be unless you tell it otherwise. Now, it underlines your questionable words in red and, when you tap on them, it offers up possible suggestions:

Wireless syncing of Notes

Remember back when we couldn't sync Notes from our iPhones to our computers at all? Now, not only do notes sync into Mail on the Mac (which I still consider to be a strange place), but they can also sync wirelessly. The Notes app on iOS 4 now associates itself with different e-mail accounts, and it can sync to your desktop over-the-air via IMAP:

Avoid crossing that monthly data cap

Many AT&T users have either downgraded their data plans or signed up with new ones that either have a 2GB or 200MB monthly cap, and some carriers in other countries have similar data consumption limitations. Because you may not want to unnecessarily use up some of that valuable data, iOS 4 now has a setting (accessed via Settings > General > Network) so you can turn off cellular data altogether if you so choose:

iBooks on iPhone/iPod touch

Following the successful launch of Apple's own e-bookstore and app on the iPad, iBooks, Apple is now bringing e-books to the small screen. iPhone and iPod touch users will now be able to use essentially the same app—designed for the smaller screen of course—to read books purchased from the store, as well as PDFs. If you also have an iPad, you can sync your books between devices, as well as your bookmarks, notes, and last read pages.

I'm not personally fan of reading books on my iPhone, but people (including many of you, dear Ars readers) seem to like it well enough—why else would the Kindle iPhone app be so popular? It's certainly convenient if you want to catch up on a book while commuting or waiting in line at the post office, and then have your place synced back over to your reading device of choice later when you go home.

Search suggestions

Like Safari on the desktop, Mobile Safari now offers search suggestions when you begin typing something into the search box. It doesn't matter which search engine you're using; depending on what the query is, you'll get a list of options that seem most similar to what you're trying to find in order to speed up the process.

I find this to be a welcome addition to Mobile Safari and am glad that Apple decided to implement this on the iPhone and iPod touch after having seen it in action on the iPad. Things work a little differently on the iPhone of course—the suggestions pop down in their own menu on the iPad, while they populate the main browser window space on the iPhone. Different sized screens, different implementations.

Bing comes to iPhone

Speaking of search feature updates, Apple has added Bing to the list of search engines that you can use with Mobile Safari. You can access this setting by going into Settings > Safari > Search Engine to choose between Google, Yahoo!, and Bing. Then, when you perform a search within Safari, your search suggestions will come from that particular search engine, as well as (obviously) the results.

People who like Bing—I hear there are a few of them—will certainly like this update. Contrary to some of the recent rumors, however, Apple has not yet made Bing the default search engine on iOS.

Customize your Spotlight searches

Nothing is more annoying than searching your phone for an app and coming up with a ton of e-mails, or searching for a contact and coming up with a bunch of songs in iTunes. Do youever use Spotlight to search for songs in iTunes? Neither do I. As it turns out, Apple had this feature in iPhone OS 3.x, but it was buried in another part of the settings (Settings > General > Home > Search results). 

Under iOS 4, you can go to Settings > General > Spotlight Search to check or uncheck all manner of content, from Contacts to Applications to Audiobooks to Notes, and everything in between. You can also re-order the content so that certain results will appear first: just tap and drag the list-like icon on the right-hand side to move the item around. Do you always want your Mail searches to come in first? Put that at the top. (Insert Steve Jobs saying "boom" here.)

On top of this customizable Spotlight setting, Spotlight can now also search the Web or Wikipedia for keywords that you enter there. While Android users have enjoyed this functionality since at least Android 2.1, this is my first experience with it and I think it's pretty much the greatest thing ever—no longer do you have to launch Safari or a Wikipedia app to look something up unless you want to.

Location, location, location

You likely don't need me to tell you that location-based services have exploded since the release of the iPhone 3GS and iPhone OS 3. Now that there are a million services (and apps to go with them) that might poll your location, Apple has responded by adding in a control panel where you can divvy up location permissions on an app-by-app basis on a single screen:

This can be found by going to Settings > General > Location Services, where you can either turn it all off or turn services off individually. On top of that, the screen also shows you which apps have polled your location in the last 24 hours, so you always know what's been keeping tabs on you. Though all apps need your permission to grab your location, all of this info in one screen is really nice to have—it allows you to get a quick look at your settings, and it keeps you aware of which apps have been pulling that sensitive information. (In addition to this, Apple has added a little pointer to the top menubar to notify you when you're using an app that is currently pulling your location info.)

Expanded enterprise support

I wasn't able to test any of these features (as I don't have accounts that I would test them with), but it's certainly worth noting that iOS 4 comes with a greatly expanded list of enterprise features aimed at business users:

• You can now encrypt your e-mail or attachments with your iPhone PIN code. The API for this is also available to developers so that you will be able to encrypt data inside of third-party apps as well.
• Apple now offers a mobile device management solution so that someone deploying lots of iPhones within a company can manage them.
• Wireless app distribution: no longer do you have to deploy apps across your company's iPhones with a physical connection. You can distribute apps to anywhere in the world from your own servers.
• As we mentioned in the Mail section, you can now have multiple Exchange accounts on a single phone.
• There's now support for Exchange Server 2010.
• There's now also support for SSL VPN.

Developers, developers, developers!

by Clint Ecker

Apple's big steps on the user-facing side of iOS are matched by, if not eclipsed by, the magnitude of new and newly opened APIs for developers.

Support for multi-tasking is one of the biggest additions, and Apple makes it very easy to add differing levels of backgrounding to applications. What most people will notice is what Apple is calling Fast App Switching. Essentially, the entire app is frozen in place nearly perfectly. Music will resume playing at the exact point it was playing when you switched away; it is literally as if someone hit the pause button on the application. All applications will gain support for this feature simply by linking and compiling their application against the iOS 4 SDK. Applications can proceed from there to take advantage of new events sent to applications which are about to be backgrounded or made inactive. Similarly, developers can perform special functions when their apps are brought back to life.

Going beyond Fast App Switching, Apple has blessed three classes of applications with preferential treatment when it comes to multi-tasking. These are VoIP, audio, and location-based applications.

iOS 4 treats each of these classes of applications slightly differently. VoIP applications will be background-launched on system boot so they are always available, audio applications will stay backgrounded as long as they play music, and Apple has provided several new methodologies for getting at location data while location-based applications are in different states.

It seems that Apple will be trying out these three types of "true" backgrounding to see how they work in practice against a wide swath of applications. The company's attention is focused on background processes that simply cannot be mimicked by using push alerts and so forth. Twitter, social networking, IM, and gaming clients can simulate very nearly any kind of real-time update by just using push notifications. Alarm-style applications now have scheduled local notifications. These are classes of applications that Apple very likely believes it has "solved" the backgrounding issue for.

Many users might insist that they need Application X to be constantly checking for new articles in the background, but do they really? When you resume the app, it's going to check in and grab anything new. Some people will complain that they might be resuming the app in a subway tunnel, but is it really necessary for Apple to focus its efforts on such a niche?

Maybe it is, and Apple will be undoubtedly looking for the next class of application it might support in these ways. However, that next tier is possibly an extremely broad group of applications—those which would like to perform arbitrary network access while backgrounded. Furthermore, it seems likely that the people demanding these features are mostly power-users, a group that Apple is comfortable with not placating when the company's energy is best diverted elsewhere.

People have begun to notice how Apple leverages its "incredible patience," manifest in the time it took to survey the landscape and roll out an extremely limited form of multi-tasking. We believe Apple will continue this practice of patience to see if even more extended forms of backgrounding are necessary.

Game Center and GameKit

by Clint Ecker

Something had to be done about the lack of a centralized social gaming center on iOS. There have been whole companies whose sole purpose has been to build such systems—ngmoco's Plus+, Chillingo's Crystal, OpenFeint X, and more—but it seems like every app uses a different, incompatible system. Apple clearly believes this is something it needs to provide in a centralized way that any developer can integrate. Developers will interface with new GameKit classes that will allow for defining in-application achievements, access to custom leaderboards, matching groups of users together based on any number of criteria, and even in-application voice chat. That's right, the technology now exists to have your sexuality called into question by a 13 year old kid while playing a head-to-head game of Angry Birds... over the Internet.

Game Center, the application, will be backed by Apple's servers and will maintain the connections between Game Center accounts with Apple IDs. People will have Game Center handles and maintain Game Center friends lists. You can find a friend and see what game they're currently playing, challenge them to one of your favorite games, and more.

Overall, there's simply too much developery goodness to go into, and much of what I could write would result in a stern email from Apple PR, but a short list of exciting things we can all look forward to are:

• iAd integration
• Quicklook previews
• Calendar and Photo Gallery integration
• In-application SMS composition and delivery
• In-application support for Captive Wireless Networks—those which need authentication before you can begin using them, like at airports or coffee shops.
• MapKit improvements: draggable annotations and custom shape and path overlays. Accelerate libraries for doing linear algebra, DSP, matrice, and vector operations. More or less a port of vecLib from the desktop.
• CoreLocation update will allow for coarser grained monitoring of position, e.g. when you enter regions or make significant location changes.
• CoreMotion is now how developers will deal with the accelerometer and get 3D space data from the new Gyroscope in the iPhone 4.
• CoreTelephony will allow applications to respond to phone call events (knowing when you are dialing or have begun a call)
• NSRegularExpression provides developers with a built-in and supported class to extract data from strings.

Finally, in a move that will provide many applications with a nice performance boost, the LLVM compiler is now included as an optional compiler for use in iPhone development.

Conclusion

Despite its flaws, the iOS 4 update is certainly a solid one with enough new features to make it worth upgrading for pretty much everyone. Trying to live without even the most basic aspects of multitasking (notably state-saving) can be frustrating once you have used it for a while—during the time I wrote this, I continually switched back and forth between an iOS 4 phone and an iPhone OS 3.x phone, so I know from experience.

Themost exciting part about iOS 4 is really what third-party developers will do with the 1,500 new APIs. After all, the iPhone experience has become one that is almost defined by its apps, and Apple has opened up a new world of possibilities with its latest API offerings. As we go into the second half of 2010, we're sure to see plenty of new apps that do creative things with Game Center, multitasking capabilities, the camera, and more.

So, unless you have a specific reason to hold back—jailbreakers, we're looking at you—or you're a poor, abandoned original iPhone owner, we can't see why you wouldn't want to upgrade your iPhone or iPod touch. We may not have covered every single detail of the new OS in this writeup, but our experience says it's well worth the upgrade.