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How does multi-tasking work in iPhone OS 4?



As expected, Apple rolled out a multi-tasking system in iPhone OS 4, and it is quite impressive. It is not, however, a thoughtless “let multiple apps run at once” proposal. Instead, they’re offering specific functions that run in the background that should keep it from being a huge drain on battery, processor and users. Updated!

First, let me admonish myself for using the term “multi-tasking”. I’ve made a point to avoid it since so many people use it incorrectly. More precisely, Apple is offering third-party apps a means of running processes in the background. The iPhone OS already “multi-tasks” with its built-in apps. The big change now is that they’re opening it to others.

The seven services now available to developers are: music/audio playback, VoIP, background location, push notifications, local notifications, task completion, and fast app switching. Apps running the background are accessible by double-tapping the home button. This pulls up a dock, like the one on the home screen, that lets you scroll and select between the apps currently open.

Audio playback is the one I’ve really wanted and the easiest to explain. Just as the iPod app can play music while the iPhone is locked or doing other things, now that same functionality can be applied to other apps, including accessing playback control from the lock screen. Anyone who love listening to Pandora knows what a pain it is to shut down the app whenever some other task arises. Well, now you don’t have to, unless that task involves playing audio.

VoIP is another easy one. If you use Skype, now you can let the app run in the background to receive calls. Furthermore, you can stay on a call while doing other things, just like the built-in phone function does.

Background location works two different ways. For apps that provide turn-by-turn directions, this services allows it to keep running while you do other things. So, if you wanted to run TomTom and Pandora at the same time, you could. Drawing GPS data like this is a big battery drain, so for activities that do not require such accuracy, apps can opt to rely on cell tower triangulation instead. They’ve also added a status bar indicator to let you know when an app is using your location and designed a new location services control panel.

Push notifications are already available in the current OS, sending you updates from a remote server. Local notifications does the same except the notices get pushed out locally, like clock alarm and calendar do, which I use all the time.

Task completion is what it sounds like. Apps can be set to finish tasks in the background after you exit them, just like the Mail app will finish sending an email after you exit it.

Finally, there’s fast app switching. This allows an app to stop in place while you do something else and resume function when you return to it. This is the only one that seems entirely new since even the built-in apps usually refresh when you come back to them.

Now before everyone gets too excited, be aware it won’t be available for your iPhone or iPod touch until summer, presumably in time for the release of the next iPhone model, and not until fall for the iPad. Also, this functionality won’t all work unless you’ve got the iPhone 3GS or 3rd gen iPod touch. You’re out of luck if you’ve got anything older.

Last thing I’d point out is this tidbit from the Q&A session regarding app management, which I read on Gizmodo’s liveblog of the event.

If you want to kill an app…you don’t have to. We architected something so the user doesn’t have to be the custodian of applications. We’ll give the apps in the foreground as needed. The user doesn’t have to worry about that at all. The user just uses things.

In multitasking, if you see a task manager, they blew it. Users shouldn’t have to ever, ever, ever think about that stuff.

This is one of a few slams against Android in the Q&A, but the point is absolutely right. I pop open the task manager in Windows all the time to kill processes. It’s not something I want to do, but it must be done. That’s always been a big strike against usability to me. I suspect the approach of limiting multi-tasking to certain background processes will be the key to making this work.

Update: There’s a YouTube video of the app switching in action. Via Gizmodo.



  1. Rob

    04/08/2010 at 2:37 pm

    that “blew it” quote actually included something quite telling that Gizmodo missed. From the gdgt live blog:

    Steve: “It’s like we said on the iPad: if you see a stylus, they blew it. In multitasking, if you see a task manager, they blew it. Users shouldn’t have to ever, ever, EVER think about that stuff.

    • Sumocat

      04/08/2010 at 2:45 pm

      Well, there goes stylus support, at least until Steve changes his mind.

      • El Lizardo

        04/09/2010 at 7:19 am

        Sorry I don’t understand the problem… if you want to use a stylus, you can use one! (they use them in the apple store for accepting signatures)

        Jobs was having a dig at other mobile software that requires a stylus. The iPhone OS doesn’t require one, but it certainly doesn’t stop you using one if you want to.

    • drphysx

      04/08/2010 at 3:14 pm

      This is ridiculous.

      This guy doesn’t understand, that the stylus is not there to replace fingers.

      It’s there to do stuff that fingers can’t do.

    • Nameless

      04/09/2010 at 12:14 am

      If I ever meet Steve Jobs, I’m going to ask him what they take signatures at Apple Stores with.

      Apparently, they decided to start eating their own dog food by replacing a bunch of old Windows CE handhelds (oh, the irony) with iPhones/iPod touches, on which you give your signature with the help of-you guessed it-a Pogo stylus!

      Even he should know that if you’re forced to write with just a fat finger, they blew it.

      • Xavier Lanier

        04/09/2010 at 10:40 am

        Actually, when I went in to the Apple Store to get my iPad I was asked to sign with my finger. Maybe Steve snatched the styluses away already.


    04/08/2010 at 3:05 pm

    sounds like much the same as what android do, except that google expects the developer to figure out what needs to be available while in the background, rather then set up special categories.

    that is, when say a android music player gets started, it has two parts. One part handles the playback while the other handles the gui. When the user then switches way from the app to something else, android knows it can throw away the gui part, but keep the playback part going in the background. As the gui state is saved before thrown away, for the user it will look as if the whole thing was sitting there doing what it was supposed to be doing the whole time.

    so the idea is the same, the difference is in the trust between google and developer that said developer will not do something “bad”, while apple have no such trust and so specify what exact task the developer can background.

    and i suspect that apple will police this harshly so that no app can game say the “task completion” to stay in the background continually. I also suspect that the “fast switch” do a state save pr default, so that if ram gets constrained said app can be removed.

  3. drphysx

    04/08/2010 at 3:15 pm

    Actually, on Androin, you don’t have to close apps, either.

    You even *shouldn’t*.

    Just let Android handle the multitasking, it works.

    iPhone OS 4.0 is better than nothing, but still FAR, FAR AWAY from catching up to Android.

  4. Joe

    04/08/2010 at 5:48 pm

    Yeah, basically Apple is doing what the Treo did in an almost identical manner with Garnet (PalmOS). I’m not really impressed, and kind ofexpected a better implementation.

    But, then again, this will probably be good enough for the iPhone users out there. Someone who cares that much about multitasking is probably using a different device anyway.

  5. nobody

    04/11/2010 at 5:05 pm

    So basically, it’s not multitasking. It’s a notification system.

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