The post above me is not quite correct, it's also not very clear what you mean.
Concerning activities and such, you'll have to distinguish between
This is basically a summary of the Android fundamentals at:http://developer.android.com/guide/topi ... ntals.html
but it took me a long while before I understood it properly.
1) One *.apk file is considered as One Application
2) By Default: Every Application runs in its own Linux Process
3) Each process has it's own Dalvik Virtual Machine
4) One Application can contain several basic components (=Activities, services, broadcast receivers, content providers)
5) All of these components are executed on the main thread (= GUI thread) (Even services!)
6) It is possible to instantiate new threads within the Application
7) One Application can make use of components of other Applications (By intents, Activities and such)
8 ) When that happens the Android OS will start the other Application and therefor instantiate a new Dalvik VM
9) A Task
is the way an user perceives and Application, it is a stack of activities which may belong to several Applications.
10) The back button causes the previous activity in this back stack
to return to focus, the most current activitiy will be killed.
Activities are managed by the OS through the Activity Life cycle:http://stuffthathappens.com/blog/wp-con ... rtical.png
In my experience the whole freeing up of memory and such doesn't work properly. It seems to me that this system needs to be tweaked to create a more usable environment. My 1.5 Android OS on the HTC Hero allows to much slowdown