Virtual machines and virtualisation

Virtualisation lets one physical computer act as several independent "virtual" computers, each with its own OS — the technology underneath cloud computing.

• A hypervisor allocates the real CPU, RAM and storage to each virtual machine (VM).
• Benefits: better hardware utilisation, isolation (a crashed VM doesn't sink the host), easy backup/cloning, safe testing of software or malware.
• You can run a different OS inside a VM (e.g. Linux VM on a Windows PC).
• Data centres rent VMs to customers — that is the core of IaaS cloud services.
• Cost: some performance overhead and licensing complexity.

• Virtual machine — a software-emulated computer running on a physical host.
• Hypervisor — the layer that creates and manages VMs.