My iPad runs iOS 4.3

If I'm playing an MP3 file in Dropbox, and then went to check news on Safari, the sound stops!

So what is the meaning of multitasking then?

The iPad's operating system, iOS, is not really a multi-tasking system in the way that PC guys think - it's more of a task switching operating system. When you switch from one app to another, the app that you've switched out is suspended and its 'context' (state) is remembered by iOS. Suspended tasks can only perform a very limited range of operations. See this Apple official link for details of what a suspended app is able to do.

What's New in iOS 4 - Apple Developer (What's New in iOS 4 - Apple Developer)

iOS leaves recently suspended apps in the iPad's memory (RAM) until it finds it needs that space for another app. Then the suspended app is overwritten but its context is remembered.

When the user switches back to a previously suspended task/app, if it's already in RAM iOS can immediately re-instate it and it 'comes alive' very quickly. If iOS had had to remove it to make room for another app, then it's reloaded from flash and brought up in the state in which it was originally suspended by using the context information that iOS stored when the app was originally suspended.

When you 'flush' a suspended app by using the multi-task bar you do a couple of things. If the app is in RAM still, its space is freed up and another app can use it. If it's already been removed from RAM then its context information is deleted and iOS will forget the state that the app was in originally. Thus, when you start that app up again, it will come up in its default state with no reference to the state it was in when it was last closed (there are some exceptions to this, however, when an app itself stores context information).

So, when you look at the multi-task bar and see all those apps 'running' all they're probably doing is having their context remembered - a few bytes for each app stored in the iPad's flash memory. Only the most recent apps - those that are shown to the left hand side of the multi-task bar - are even candidates to be in RAM. You can usually tell which apps were in RAM by the time the iPad takes to switch back to that app when it's re-instated. Those that are 'down the list' to the right, or even on the next screen, were long ago removed from RAM.

Tim

Audio apps need to be coded in such a way, that they can continue playback while in the background. Because as Tim mentioned, apps get frozen when in the background, so the whole app will stop, including any audio. Apple provided a workaround for audio, but the support has to be coded into the app.

That said, some programs can be convinced to continue playback, by pressing Play after the app has been minimized. To try this, enter the Multitaskbar, slide to the left and press play. It may or may not work.