Understanding JVM: Introduction

What are Virtual Machines?

Virtual machine is something which does not have a physical existence, for example, PC calculator. In other words, it is a software simulator of a machine that can perform operation like a physical machine, hence the name - Virtual Machine.

Types of Virtual Machines

There are 2 types of virtual machines:

1. Hardware based / System based:  These are multiple logical VM, independent of each other, working a single physical VM, example of the same are Kernal Based VM (for Linux), VMware, Cloud Computing, etc. Hardware based VMs results in effective utilization of resources. However it is more related to admin terminology, not programmer.
2. Application based / Process based / Software based:  These VMs acts as run-time engine to execute a particular programming language application. Example: 
• JVM - For Java
• CLR - For .net
• PVM - For Parrot (scripting language)

Basic architecture Diagram of JVM

JVM is the run time engine to execute Java applications and is part of JRE. It loads and executes application line by lines.

Following is the basic architecture diagram:

Different components in the above diagram will be explained in the coming tutorials. Go to Class Loader Sub System to read first component.