Android isn't "close" to linux, it IS linux.. that is the OS that runs on all android phones is a linux kernel, 2.6.x. Android is a platform that runs on top of the linux kernel and handles the task of starting up individual Dalvik JVMs for each app you run. Each and every app you see running in your task list is a separate JVM instance all to itself, so that if the app crashes the JVM, it ONLY brings down that one app. The phone still works, as do the other apps. Each time you install an app, it's installed as a separate user as well. So each app you run, runs as it's own separate user too, making it that much more secure from one app to the next.