There are two kinds of background processes in Android (unless it's changed since I last wrote an app, which is possible - that was for OS 1.5).
This article is describing how the main app (the bit you see) functions. When it is swapped out you get an event, then again if they are killed. The OS manages that.
However you can also write services/daemons which are persistent and (as far as I know) not suspended by the operating system. I don't believe they can present a UI but they can communicate with your main app.
These are intended for things like occasional server polling and pushing notifications to the bar. But I don't believe there is any technical restriction on using them for other things.
This article is describing how the main app (the bit you see) functions. When it is swapped out you get an event, then again if they are killed. The OS manages that.
However you can also write services/daemons which are persistent and (as far as I know) not suspended by the operating system. I don't believe they can present a UI but they can communicate with your main app.
These are intended for things like occasional server polling and pushing notifications to the bar. But I don't believe there is any technical restriction on using them for other things.