See the original posting on JavaWorld
The Java virtual machine is a program whose purpose is to execute other programs. It’s a simple idea that also stands as one of our greatest examples of coding kung fu. The JVM upset the status quo for its time, and continues to support programming innovation today.
Use and definitions for the JVM
The JVM has two primary functions: to allow Java programs to run on any device or operating system (known as the “Write once, run anywhere” principle), and to manage and optimize program memory. When Java was released in 1995, all computer programs were written to a specific operating system, and program memory was managed by the software developer. So the JVM was a revelation.