How to prevent apps running in background Possible Duplicate:
  How can I stop applications and services from running?  




i've an Xperia X10 Mini. This Android devices is limited in hardware: a 600Mhz processor and 128 mb ram. So i'd like to install new apps, but i don't like to have a lot of apps running in background. For example, Facebook app, GDrive, Dropbox ... are great, but why 'damn' thei must run in background either if i don't want to use them at the moment ? This cause my device to run slowly, very slowly... 

I know that facebook app for example, 'must' stay in background so it can inform me for a new 'friend post' .. but i don't need it! 
Also Gdrive, Dropbox, Gmail etc: they 'must' stay in background to inform me for something.. but i'm not interested !!! If i want to check mail... i click to gmail.. if i want to check my friend post... i click facebook !

What i want is a responsive smartphone for basic operation (call, sms etc.), and i'm sure a 600mhz processor with a basic 'android'  installation and without background app  can go fast as a double core Arm with 100 running app !!!!

So, at the moment i disinstall them, and my device back to run good, with no slowdowns.

I also have installed Advanced Task Killer, but it kills apps each hour, or 30minutes: it don't prevent an app to run in background. 

Does exists an app that kill others app each time they start in background, immediately ?
Though there are apps around that would answer to your request (so-called "Task-killers" and "Memory boosters"), their usage is not to recommend -- simply because it would not help any (see Is it advisable to run a task killer app on Android). If those background processes are designed as services, they would simply restart - as would many other apps as well. Usually Android handles RAM very well, and those background processes should not use significant CPU power -- so on a decent phone this should not be a problem. However, on low-end and small devices with just minimal RAM and CPU, this can become an issue.

So what are your choices then? First, you could see to uninstall all those apps running background tasks -- provided you do not really need them. And, of course, if your device is not rooted, this cannot be done for pre-installed apps; but with ICS and higher you can at least "freeze" them.

If your device is rooted, your choices increase dramatically: you can remove (or freeze) those apps e.g. using Titanium Backup. You can use managers like AutoRun Manager to modify intent-listeners of apps (to prevent the start of certain event-based background processes, including those started on boot_completed). And you can configure thresholds for how your RAM will be used (i.e. when Androids internal Out-of-Memory-Killer should clean up your RAM) using apps like AutoKiller Memory Optimizer (don't mistake that name with a task-killer, it is not) or Auto Memory Manager.

Of course, you can also ask the developer to make those background services configurable -- and to leave it to you whether certain of them should be running at all. There's always the chance the developer sees reason and implements such a feature.