How does multitasking in iOS4 actually work?

It’s not true multi-tasking. I believe from reading that it puts the program on “hold” therefore not draining battery power. When you go back to the program it resumes where you left off.

It does take more battery to multi-task, this applies to any computer. The more the CPU has to process the more power it is going to take. Running a CPU at 100% will take more than running the CPU at 25%.

@missingbite I believe on the new iPhones they do multi-task, older generations do not, same applies with like the new HTC EVO. You can, at the same time, play music, surf the web, download apps, and talk on the phone and they are not on “hold”.

@Tenpinmaster Also when it comes to phones, many things effect the battery life, such reception, usage, environmental factors etc. For example using 4G takes more power than using 3G. Also it takes more power to make the connection if the signal is weak. The better the signal, the less power the phone will use.

First, all iPhones have always multi-tasked. iPod music playback in the background, phone calls while web browsing, etc.

Up until iOS 4, the limitation was that 3rd party, non-Apple apps could not execute in the background.

Now, with iOS 4, there are only very certain tasks that a 3rd party app can perform in the background:
1) audio, e.g. Pandora Radio
2) phone calls, e.g. Skype
3) notifications
4) location services, e.g. TomTom GPS

Further, the full app isn’t running in the background. Only a single thread is active to handle one of the 4 situations above. That’s where the battery savings come from.

Fast task switching, another touted feature, is not multi tasking. It works similar to how Mobile Safari has in earlier versions of the OS. Apps that are backgrounded are paused while there’s enough RAM. Paused apps still in RAM can resume where you left off quickly. Paused apps out of RAM are stopped just as in earlier OS’es. An app’s stopped behavior is up to the developer. Some pretend to be paused, others make you start over. Nothing new there.

@robmandu thank u very much. That’s exactly what I needed to know! :)

Thank u everybody for ur participation in answering my question