What is Java Virtual Machine or JVM ?

Java Virtual Machine

JVM is the main component of Java architecture and it is the part of the JRE (Java Runtime Enviroment) . It provides the cross platform functionality to java. This is a software process that converts the compiled Java byte code to machine code. Byte code is an intermediary language between Java source and the host system. Most programming language like C and Pascal converts the source code into machine code for one specific type of machine as the machine language vary from system to system . Mostly compiler produce code for a particular system but Java compiler produce code for a virtual machine . JVM provides security to java.
The programs written in Java or the source code translated by Java compiler into byte code and after that the JVM converts the byte code into machine code for the computer one wants to run. JVM is a part of Java Run Time Environment that is required by every operating system requires a different JRE .
The architecture of the JVM is given below . This architecture tell us how the JVM works . Firstly we write the simple java program(source code) the java compiler converts the source code into the bytecode , after that JVM reads this bytecode and converts this into the machine code.

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Acronym for Java Virtual Machine. An abstract computing machine, or virtual machine, JVM is a platform-independent execution environment that converts Java bytecode into machine language and executes it. Most programming languages compile source code directly into machine code that is designed to run on a specific microprocessor architecture or operating system, such as Windows or UNIX. A JVM -- a machine within a machine -- mimics a real Java processor, enabling Java bytecode to be executed as actions or operating system calls on any processor regardless of the operating system.
For example, establishing a socket connection from a workstation to a remote machine involves an operating system call. Since different operating systems handle sockets in different ways, the JVM translates the programming code so that the two machines that may be on different platforms are able to connect.

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A Java virtual machine (JVM), an implementation of the Java Virtual Machine Specification, interprets compiled Java binary code (called bytecode) for a computer's processor (or "hardware platform") so that it can perform a Java program's instructions. Java was designed to allow application programs to be built that could be run on any platform without having to be rewritten or recompiled by the programmer for each separate platform. A Java virtual machine makes this possible because it is aware of the specific instruction lengths and other particularities of the platform.
The Java Virtual Machine Specification defines an abstract -- rather than a real -- machine or processor. The Specification specifies an instruction set, a set of registers, a stack, a "garbage heap," and a method area. Once a Java virtual machine has been implemented for a given platform, any Java program (which, after compilation, is called bytecode) can run on that platform. A Java virtual machine can either interpret the bytecode one instruction at a time (mapping it to a real processor instruction) or the bytecode can be compiled further for the real processor using what is called a just-in-time compiler.