Multitasking

[ibensi01]

How many third-party applications can the iPhone 3GS and the iPhone 4 reasonably run simultaneously?

 

[Gregoris]

I usually have 8-9 apps open and it runs fine, my brother never closes any app and has them all open in the background and it still runs fine

 

[Bigdave]

i have in excess of 40 apps open the multitasking is flawless, still runs amazing even though the battery life takes a bit of a slamming :S

 

[Gregoris]

It does have a good amount of ram and processing speed

 

[iCrank]

It does have a good amount of ram and processing speed

Better than the iPad.

 

[Bigdave]

It does have a good amount of ram and processing speed

Better than the iPad.

amen..

 

[Skull One]

How many third-party applications can the iPhone 3GS and the iPhone 4 reasonably run simultaneously?

That question is unanswerable as stated.

Now I can give you insight to the whys and that might hopefully allow your to formulate either a better question or at least an idea of the answer you are looking for.

iOS 4 doesn't run applications simultaneously. It runs them in a round robin configuration. Each application is given a finite time slice to operate within. The foreground application, the one you are actively interacting with, gets the lion share of the time. Now the rest of the time is used up by iOS or any application that has registered itself for background execution.

Now the next thing to cover is that applications need to be loaded into main memory. There is 513 Megs in the iPhone 4 and 131Megs in the iPhone 3 for this purpose if memory serves. If the average application is 20 megs in size than you can load roughly 25 apps in the iPhone 4 and 6 in the iPhone 3. But that only covers the application memory requirements. If the application has data it needs to load into memory as well, then those numbers can change dramatically. And since every application can have its own unique size, it makes calculating what you can fit in your particular device rather difficult.

Now the last thing to add to this is, as you load applications iOS looks at the memory needed vs how much memory is free. If the app will fit, then it doesn't touch any of the other application loaded. If the app won't fit it quickly runs an algorithm to decide which app needs to be unloaded to allow the new app to load. This algorithm takes into account how many times the app has been used in this memory run, if the application has requested hooks to the background subsystem and how recently this app was last used.

As you can see your question has at least 5 major factor that have to be considered before a reasonable answer can be given.

 

[FogIslandGames]

Just to add to the post above, I would say watch for splash screens or other tells. A good app should be able to recover from a background kill and pick up where it left off. But sometimes you will see a splash screen or something that lets you know this is being spun up, not just placed back into memory. Some apps are very demanding and will kill all background apps (puzzle quest 2 as an example) while others are so small in footprint you could have dozen's running without an issue. It just really all depends on what apps you use.