Virtualisation

In short: Virtualisation means that several separate “virtual” computers, called virtual machines (VMs), run on one physical computer.

In more detail: A piece of software, the hypervisor, divides the real computer’s (host’s) CPU, memory, storage and network among the VMs (guests). Each VM has its own operating system and does not notice the others.

In Depth

• Hypervisor: type 1 runs directly on the hardware (e.g. Proxmox, VMware ESXi, Hyper-V), type 2 as a program inside a normal operating system (e.g. VirtualBox).
• Advantages: better use of the hardware, quick copies and backups (snapshots), separate systems for testing and security, easy move to other hardware. The basis of the cloud is virtual servers.
• Containers: a lighter form in which programs share the operating system kernel, see Docker. They start faster and need less space but are isolated less strongly.
• Use: consolidate servers, keep old software running, try a second operating system, test risky programs in a sandbox.
• Disadvantages: some loss of performance, and the host is a single point of failure.

See also: instance, Linux, Windows