Virtualization means running several sub-operating systems simultaneously on a single hardware and a main operating system.
The main operating system is called the host (main computer). All other sub-operating systems are called Guest.
The aim is to be able to make optimum use of ever faster and more powerful hardware, thus saving hardware costs, energy costs, space and peripheral costs without compromising secure and active operation.
Several systems are available for virtualization. This article describes the open source systems that are already so mature that they represent serious competition to the established top dogs.