A virtual machine may be a software implementation of a machine (i.e. a computer) that executes programs sort of a physical machine. Virtual machines are separated into 2 major categories, supported their use and degree of correspondence to any real machine. A system virtual machine provides a whole system platform that supports the execution of a whole operating system (OS). 

Virtual machines are used to produce an environment separate from the host operative environment. As every machine works independently with its own storage and process power, one server will have multiple such environments. Users will use them to make and test applications without worrying concerning affecting the host operating system. 

There’s no threat of work obtaining halted if the machine crashes down. Because it is separate from the principal, it may be rebooted and work may be carried out usually. This permits lots of flexibility and engineering power to the users.

In distinction, a process virtual machine is intended to run one program, which implies that it supports one process. a vital characteristic of a virtual machines is that the software running inside is limited to the resources and abstractions provided by the virtual machine—it cannot break out of its virtual setting.