What is a Virtual Machine?

A virtual machine is actually commonly described as an implementation of a software on a machine which is described as computer. Instructions on this virtual machine can easily be executed just like as these are executed on the physical machine. This type of computer machine was originally described as an isolated, efficient duplicate of a physical machine and this definition was given to it by Goldberg and Popek.
Virtual machines that are currently in use all over the world physically have no direct connection or correspondence with any kind of device which is known as hardware to perform. This technology type is described in two different categories and these categories are defined because of their usage and amount of correspondence which is made through it with any real or physical machine.
These two categories of a virtual machine are widely known as a process virtual machine and the name of second category is a system virtual machine. A complete platform of a physical system is provided by the system virtual system and in this type an operating system on a physical machine can be fully executed with through system virtual system.

But the second category of virtual machine which is known as a process  virtual machine is actually prepared in order to perform any single task or to run a single program on a physical or real machine which clearly means that only a single process can be supported by a process virtual machine at a time. Software that run inside a virtual machine are limited in terms of its resources