Virtual machine is a program that has the same functionality as a physical computer. Java bytecode is the result of the compilation of a Java program, an intermediate representation of that program which is machine independent. The Java bytecode gets processed by the Java virtual machine (JVM) instead of the processor. It is the job of the JVM to make the necessary resource calls to the processor in order to run the bytecode. Computers vary in the hardware they use, and run different programs and operating systems. Sometimes we might want to have the functionality and capability of another computer system running on our own computer. It may be that the hardware for the other system no longer exists or is unavailable, or we may wish to have several versions of a computer running simultaneously on one hardware system.
We can use software to emulate the other computer system so that our computer can behave like that system. This emulation is known as a virtual machine. The process of creating and running a virtual machine is known as virtualisation.
The computer that runs the virtual machine is known as the host. The virtualized system is known as a guest. Virtualisation software, known as an emulator, creates a virtual implementation of the guest system on the host computer, providing the host with the functions and programs of the guest. The emulator translates the instructions of the guest computer so that the host computer can understand them.