JVM is a just program which runs on a machine.So you can run multiple copies of the same program. It's just as you open multiple command prompts. Although you execute the same physical file for the command prompt, they are different instances with different processes
You may multiple JVM's without noticing it. For example, you could run weblogic, have SmartCvs running for your source control and IntelliJ Idea as your
IDE. In this case, you have 3 instances of the JVM.