Until the release of iOS 4, the iPhone could – with a very few exceptions – only run one app at a time. Ever since, though, iPhones (and other iOS devices) running iOS 4 or higher can take advantage of multitasking and run multiple apps at once.

Or can they? Despite the hype about the introduction of iPhone multitasking, this isn’t the multitasking we’re used to. Here’s what you need to know.

Not Your Father’s Multitasking
In the traditional sense that we’ve become accustomed to on desktop computers, multitasking means being able to run more than one app at the same time.

Apps don’t quite work like that. Instead, with some exceptions based on the kind of apps and the OS, apps don’t run at the same time, instead, they switch very quickly.

Fast App Switching
Instead of offering traditional multitasking, iOS 4 and higher uses something Apple calls Fast App Switching. What this means is that, when you click the home button to leave an app and return to the home screen, the app essentially freezes where you were and what you were doing and brings you back to it when you launch the app again. So, instead of starting over each time, you pick up where you left off. This isn’t really multitasking, but it’s a nice user experience.

But Some Apps Run in the Background
In iOS 4 and higher, there are a few types of apps that can run while other apps are also running (aka, running in the background). This is more the traditional multitasking that we're used to. Apps that can run in the background fall into a few broad categories:

• Music – so you can listen to the Music app, Pandora, streaming radio, and other music apps while doing something else.

• Location – Apps like GPS that would allow you to listen to music and get directions simultaneously.
• AirPlay - Apple's tool to stream audio and video from the iOS to compatible TVs, stereos, and other devices can run in the background while you run other apps on your iOS device.
• VoIP (Voice Over IP) – Apps like Skype that let you make phone calls over the Internet instead of over the 3G cellular network.
• Push Notifications - These notifications tied to apps let you know something's happened in the app that you'll want to check out. They usually take the form of a red circle with a number in it attached to the app icon.

Just because apps in these categories can run in the background doesn't mean they will. The apps have to be written to take advantage of that iOS 4 feature – but the capability is there in the OS and many, maybe even most, apps in these categories can run in the background.

In iOS 7, apps that can run in the background are even more sophisticated. That's because iOS 7 is smart enough to learn how you use apps. If you usually check your social media feeds first thing in the morning, iOS 7 can learn that behavior and, in the background, update your social media apps a few minutes before you normally check them to ensure that all the latest information is waiting for you.

How to the Access App Switcher
To access the Fast App Switching tool, quickly double-click the home button on the center of the iPhone’s face. What happens at this point depends on what version of the iOS you're running. In iOS 4-6, this will gray out most of the screen and reveal a set of icons at the bottom. You can swipe the icons left and right to see the apps installed on your phone. Tap on an icon to launch that app.

On iOS 7 or higher, the entire screen drop back a bit to reveal a set of mini screenshots and app icons for all running apps. Swipe left and right between them and then tap the app you want to use.

Killing Background Apps in App Switcher
The Fast App Switcher also allows you to quit apps and, especially their background processes. This can be especially useful if an app isn't working properly or may be downloading data in the background when you don't want it to. Killing background apps for third-party apps will stop them functioning completely, at least until you relaunch them. Killing Apple apps will allow them to continue their background tasks (like checking email), but will force them to restart.

To kill apps, open the Fast App Switcher. In iOS 4-6, tap and hold and app icon until the icons begin to jiggle and a red badge with a minus sign in it appears on the apps. Tap the red badge to quit that app. You can do that with as many apps as you'd like to close. This will not delete the apps from your device (just quit them).

In iOS 7, instead of tapping the app, swipe it up the screen. This causes the app to disappear and be quit. You can tap and hold on up to three apps at once and swipe them up at the same time. By doing this, you can kill multiple apps at once. How's that for efficiency?

How Apps Are Sorted
Apps in the app switcher tray are sorted based on what you used most recently. This is done to group your most-used apps together so you don’t have to scroll too much to find your favorites.

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