Virtualization separates an operating system instance from the underlying hardware. Virtualization allows you to move operating system installs from one piece of hardware to another by copying a file. Virtualization needs an operating system installed on the hardware, but that install is normally very minimal, has no public-facing services, and is easily reproduced on new hardware. It’s perhaps the biggest change in system administration in decades.

Virtualization is something like a client-server environment. The hardware and its core operating system instance is the host, while the clients are all virtualized operating system instances. ...

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