Modern machines do not consist of multiple levels of virtual machines; that is a function of the host operating system's virtual machine manager and its guest operating systems, all of which are implemented through software. The operating system's virtual machine manager exposes one or more virtual machines upon which you can host one or more guest operating systems and their applications. In order to execute compiled Java applications upon one of these guest operating systems you will also need to install the Java virtual machine for that specific operating system. Thus you end up with a Java program executing within a Java virtual machine executing within a virtual machine executing within a virtual machine manager executing upon the physical hardware. The physical hardware itself may be optimised to handle virtual machine managers more efficiently, but the virtual machine manager is a software program; it is not part of the physical machine architecture

Java virtual machine

Java virtual machine

A virtual machine will provide generic hardware that can be found in many other computers. Having a virtual machine eliminates the need to have either a second system, or to reboot to test their operating system.