How iOS Multitasking Really Works

Macworld’s Fraser Speirs notes that there’s one bit of iOS misinformation that he keeps hearing, to wit: even supposedly authoritative sources such as Apple Geniuses don’t seem to get it about how multitasking works in iOS.

The erroneous assumption Speirs refers to is that all those apps in the multitasking bar on your iOS device are currently active and slowing it down, filling the device’s memory or using up your battery, and that in order to maximise performance and battery life, you should kill them all manually.

In fact, he observes, the iOS multitasking bar does not contain a list of all running apps, but rather a list of recently used apps, which, with a few exceptions, are not currently running. Ergo, when you press the home button, in almost all cases, the app quits, stops using processor time (and hence battery), and the memory it was using is recovered, if required.

Speirs asys iOS apps can exist in any of five states of execution, Not Running, Inactive, Active, Background, and Suspended, and he explains the distinctions at some length in the article.

The confusing part, he suggests, is that none of these states are reflected in the multitasking bar, which merely shows a list of recently-used apps, regardless of whether they’re in the Background, Suspended, or Not Running.

Spiers contgends that consequently, the user never has to manage Background tasks on iOS, and that if someone tells you that all the apps in the multitasking bar are running, using up memory or sucking power, they are wrong. The system handles almost every case for you without your active involvement. I guess that’s why I can keep twp-dozen or more apps open on my 16 GB iPad 2 and not notice any diminishment in responsiveness.

Repeat: You Do Not Need to Manually Manage iOS Multitasking

Daring Fireball’s John Gruber weighs in on the iOS multitasking issue, citing Fraser Spiers’s layman’s explanation of why the misconception that all those apps showing in the iOS multitasking bar are running and eating memory space and battery life is wrong.

“Bottom line,” says Gruber, “the iOS multitasking bar is not like the command tab switcher on Mac or Windows. It is not a list of currently running applications. It is simply a list of your most recently used applications, whether they’re running in the background, suspended in memory, or completely inactive… [so] emptying this list of applications is simply needless, mindless, busywork. It was absolutely never intended to be used this way and anyone who does this is just wasting their time. The system suspends apps running in the background automatically. The system removes suspended apps from memory automatically, when needed. Manually zapping all apps from this list is a voodoo placebo.”

Gruber observes that the whole point of iOS’s multitasking model is that users should not have to worry about managing which applications are running and which are not, and that if you were supposed to do that, apps would have a Quit command, and they don’t.

For the full commentary visit here:
http://daringfireball.net/2012/01/ios_multitasking