How iOS Multitasking and Backgrounding Really Works [Video]

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Posted January 6, 2012 at 8:15pm by Shalom Levytam

Developer Fraser Speirs has created a nice video that shows how iOS manages memory when backgrounding and multitasking.

The video is in followup to a post on his blog which addresses a misconception with iOS where users believe that clearing out their multitasking bar will improve the performance of their device.

TNW notes that there are five sections to Speirs' video:
● An app going from active to background to suspended
● Instacast HD requesting extra background time to finish a podcast download
● TomTom running indefinitely in the background
● Batman Arkham City Lockdown and Real Racing 2 HD competing for big chunks of device memory
● Batman Arkham City Lockdown forcing several smaller apps out of memory

Take a look at the video below...

[via TNW]

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budsal - January 6, 2012 at 10:05pm

Fraser Speirs says, "Except in a few cases, which I'll explain, the apps that appear in the multitasking bar are not currently running. When you press the home button, iOS will tell the app to quit. In almost all cases, it quits, it stops using CPU time (and hence battery) and the memory it was using is eventually recovered if required." I'm confused. I use SBSettings - Statusbar Free Mem. When I close an application using the home button I don't seem to get the memory back until I use the multitasking bar or the function within SBSettings to close the apps. That much could be explained by the "eventually recovered if required" bit at the end, but I don't get it. For example my free mem states I'm at 336mb. Now I opened a bunch of apps and closed each with the home button before opening the next. Now I'm down to 14mb and my iphone is so sluggish that if I didn't know any better I'd think my phone is frozen and I need to power cycle. Now it just jumped back up to 46mb. So I guess that's the recovery, however minimal. I don't get it

budsal - January 6, 2012 at 10:07pm

and now with nothing in background I only have 277mb not over 300. I think the highest I've seen is something like 346mb.

Ash - January 6, 2012 at 10:34pm

The memory will not recover untill it is needed to. You could open say 10 or 15 apps leaving you with 50mb memory left then when iOS needs more it will start clearing the memory from the oldest app open. It's CPU whic IOS not used by an app when its bsckgrounded. If an app didn't use memory when bsckgrounded you'd never be able to restart the app where you left off. If you get me?

Ash - January 6, 2012 at 10:39pm

As he is trying to prove apps that are bsckgrounded dont use CPU so no battery drain. Also you won't regain your memory from simply pressing the home button as this saves the apps state in menory, but if you close it from the multitask them this will start clearing space in memory. Hope this helps.

budsal - January 6, 2012 at 11:04pm

yes that does help a lot. thank you

Nick - January 6, 2012 at 9:46pm

Well done! This really explains it clearly. Do you think there is a difference in a jailbroken device and a non jailbroken device in respect to apps staying in suspended state?

Thunderbyte - January 7, 2012 at 2:44am

If the programmer linkes it, JB Apps can and will run indefinitely (e.g. SBSettings or Intelliscreen). So a lot of persistent JB Apps CAN and WILL make the iOS device slower.