Virtualization refers to the use of software to simulate portions of a computer system.
Virtualization presents the simulation of a guest machine via special software running on a host machine.
Forms of virtualization:
a.k.a., emulation
These include the first virtualization systems (IBM 1966), often used to avoid/delay porting large application systems.
More modern instances:
a.k.a., OS-assisted virtualization
Architectures:
Runs the simulation as a host OS application.
The simulator is a “thin” OS sitting on top of the hardware.
Instances:
chroot
docker
hosted on Windows can virutalize wither Linux or Windows (but not both)