Ever realized when you long press the home screen, it shows you the last 6 apps, right? Those are the ones in memory for faster reloading. Once the app moves to spot 7 it goes idle, closes, or sticks in the background (what Romeo calls bad apps) depending on its properties.
Android's Memory management Android was designed to be a multitasking, fire-breathing beast. It allows applications to keep their spot in device RAM, and stay ready to jump back into focus when the user needs them. The OS also is very good at sharing libraries between applications, so that app coders have a great set of functions already built to choose from. In a perfect world (perfect for developers anyway) we all would use the same applications for the same reasons and that would be the end of it.
But nothing's perfect
We all use different apps, at different times, in different ways. When you consider that nightmare for developers, it's surprising that Android (or any mobile operating system) handles the job as well as it does. Let's take a quick and hopefully easy to understand look at what goes on behind that screen.
An application starts, either because you started it or the developer sees a benefit in having it run behind the scenes. Some examples of the last bit -
- When you add or remove an application, Google Voice starts (if it was not running). It scans the application to see if needs to use or share any functions with it. Install a new text-to-speech engine? Google Voice will use it.
- Copy some pictures from your SD card to your computer? The gallery needs to start up when you remount your SD card to check for new pictures or videos so it can scan them and have them ready to show in the right spot.
This all sounds great. What we aren't considering above is that these apps will stay in the device memory until they are told to close. They won't use any other resources, just sit idle and be ready to re-draw themselves on your screen. In today's age of 1Ghz+ processors and high speed data transfer, we get impatient when we want to load a NEW application and it's not instant. We want our device to zoom between screens. We want our device to snap new applications into focus. We want our device to perform in ways it wasn't really designed to do. Using a task killer the correct way can get close to those goals.
A quick study here on just how Android manages memory - Each application has a number (from 1-6) assigned to it, depending of the type of app and it's state. Android assigns a level of minimum free RAM for each category and kills off what it thinks is no longer needed in each once that threshold is reached. This is a pretty technical discussion, and I'm just going to mention it here for those that are interested. If you would like to manipulate these numbers yourself, feel free to give me a holler and I'll point you in the right direction. But let's not clutter up this any more than necessary, as this is a pretty advanced discussion.
The task killer interface
Each application looks and acts a little different, and task killers are no exception. I'll be using Advanced Task Manager for my examples. I am not recommending this above any others. It suits my needs and was well worth the $0.99, so I stopped looking for alternatives. Your choice could look a bit different, but should have the same functionality. Just have a look through the settings and you'll find where to make the same changes and choices.
Below you're looking at a list of running application that the task killer has permission to kill once you give it the go-ahead. You're not seeing every running process, and reading a little further will explain why that's a good thing. We'll refer back to this image in a bit, but take a second and look over it for now.
Manually killing tasks
The best easiest least complicated way to use a task killer is to open it and manually kill off things you're sure you don't need whenever you feel things have slowed down. The trick is knowing what else won't work if you kill off an app. Things like games, web browsers, dictionaries or other stand alone apps are usually a safe bet to kill off if you find them running. In the example above Astro File Manager is running because I was looking for a file I had downloaded. I'm done with Astro, so there is no need for it to stay running. I could safely kill it off, and nothing else would be affected.
Note
What a difference, battery life is 2-3 times what it was, NO reboots, phone is "zippy". 
