Why does Android need a Virtual Machine(DVM)?

Question

Virtual Machines are used for running apps on different OS(Java compiles code into OS independent .class files which is interpreted into bytecode). Since android apps run on the same OS (i.e Android), it doesn't require a VM (I could be wrong here). Then why does it need a Dalvik VM?

Answer 1

Android Platform can run on different architectures - ARM, MIPs and x86. To abstract out the need to compile binaries for each architecture VM comes into play. It also does memory management for the developer.

Answer 2

We need someone to compile and convert the java classes into bytecode which can be executed by the interpreter.

It is similar to JVM ... you have .java files which will be compiled by java compiler into .class files. the .class files are nothing but bytecode which will be run by the JVM. JVM can reside on any platform(windows,linux or unix).

In android too the files are compiled into .dex files and run by DVM. just to give an idea, when is application is installed, the Android OS assigns unique linux user id, a DVM is assigned for each app. So in short each app has own linux process, DVM and linux user id.

The java files are compiled into .dex files which consume less memory compared to .class files.

Now assume 10 applications are having 10 individual DVM's and the OS has 10 process to handle.

The dispatcher or scheduler in the android OS is responsible for handling these 10 processes....which is why we have android activity life cycle.

You need DVM to maintain the running state of each process(each app).