The Java Virtual Machine or JVM is an abstract or a virtual machine whose purpose is to run JAVA programs and the programs written in the other languages (compiled to Java Bytecode). It was originally designed to enable the application programs to be built with a flexibility to run on any platform without any need of rewriting or recompiling for every separate platform. It can be divided into three parts.


THE JAVA VIRTUAL MACHINE IN THREE PARTS
The JVM Specification:

The JVM is a software specification where its working is specified. However, the execution provider is completely authorized to choose the algorithms.

The JVM Implementation

The right execution of the SPECIFICATIONS results in an actual software that is called JVM implementation, known as JRE (Java Runtime Environment). There are so many implementations, of both open source and proprietary.

The JVM Instance:

Once, JVM Specification is implemented correctly and published as a software product, it can be downloaded and run as a program. This downloaded program is JVM instance.

WHAT DOES JAVA VIRTUAL MACHINE DO?
The Java Virtual Machine performs several operations including Loading code, Verifying code, Executing code and Providing Runtime Environment. However, it has two primary functions:
1.Allowing Java programs to run on any device or OS
2.Managing and Optimizing Program Memory

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