Mac Cub

One of the new features released with the iPhone 4 update is multitasking, which theoretically allows multiple apps to continue running in the background even when you’re not actively using them. On your Mac, for example you can print your Pages document while updating your Numbers spreadsheet and listening to Adam Lambert in iTunes. 

Multitasking on the iPhone and iPod Touch works a little differently than it does on the Mac. You can only see one app at a time, and there are a limited set of actions an app can perform while it is in the background. And, app developers must explicitly add those actions. If they don’t add those actions, their app will simply stop - just like it did before.

To use multitasking on your iPhone or iPod Touch just run some apps. For the most part, you shouldn’t need to be concerned about which apps are running and if this will affect your battery life. Apple designed multitasking so that it would have minimal impact on battery life. If you want to see which apps are running, double-press the Home button. This will pop up a small grid of four app icons at the bottom of the screen. You can scroll the grid left and right to see more apps. The apps in this grid are the apps that are currently “running” in the background. Again, app developers must explicitly add support for multitasking in order for their apps to actually do anything in the background. Simply tap the application you want to use. This also gives you a way to quickly switch back and forth between applications you’ve recently used - great for copy/paste. As a bonus scroll the grid all the way to the left and you will see iPod controls for pausing and moving to the next track and previous track. In addition, there’s a new icon on the far left - pressing this will turn off screen rotation for all apps.

What if you’re concerned about certain apps running in the background and you want to stop them? Open the multitasking grid, then tap and hold the app icon. The icons will start to jiggle and display a red stop icon in the upper left corner. Tap this red icon to make the app stop.

Do you really need to be concerned with apps running in the background? Not really. The actions an app can perform are pretty limited. This is what they can do:

• Background audio
• Voice over IP
• Background location
• Push notifications
• Local notifications
• Task finishing
• Fast app switching

If you want to read more about what these actions are, check out this page.

What about an app like Pandora that streams music? Pandora will continue to run even when it is not the active app, using the new Background audio multitasking feature. This allows you to continue listening to your Pandora station while you perform other tasks. Yes, Pandora will continue to use battery power as it streams music, but you still don’t need to worry about it. Simply unplug your headphones and Pandora will go to sleep. This is not to say that all apps will behave as nicely. An app like Glympse, which broadcasts your current location to all your friends, will continue to run in the background and drain your battery very quickly. This is an app you might consider closing when you’re done with it.