A hypervisor, or virtual machine monitor, is system software that creates and runs virtual machines by abstracting and partitioning a host’s physical CPU, memory, and I/O resources. Type 1 (bare-metal) hypervisors run directly on hardware, while Type 2 (hosted) hypervisors run atop a conventional operating system. By isolating multiple guest operating systems on shared hardware, the hypervisor is the foundational technology of server virtualisation and cloud computing.
- A Hypervisor is the Virtualisation software that creates and runs Virtual Machines by partitioning a host’s CPU, memory, and I/O.
- It uses Hardware Abstraction and Memory Management to isolate multiple guest Operating Systems on shared hardware.
- It is the foundational technology of Cloud Computing and server consolidation.
Overview
- The hypervisor sits between physical hardware and one or more guest operating systems, presenting each guest with the illusion of dedicated machine resources.
- Type 1 (bare-metal) hypervisors run directly on the host hardware for maximum performance and isolation, common in data centres and cloud platforms.
- Type 2 (hosted) hypervisors run as an application on top of a conventional operating system, convenient for development and desktop use.
- The hypervisor schedules virtual CPUs onto physical cores, virtualises memory through nested page tables, mediates device access, and enforces isolation so a fault or compromise in one guest does not affect others.
- Modern hypervisors exploit hardware virtualisation extensions to reduce overhead, and support live migration, snapshots, and dynamic resource allocation.
Mechanisms
- CPU virtualisation: scheduling virtual CPUs and trapping privileged instructions.
- Memory virtualisation: nested or shadow page tables mapping guest to host memory.
- I/O virtualisation: emulated, para-virtualised, or pass-through device access.
- Isolation: strong boundaries between guests for security and fault containment.
- Lifecycle features: Snapshot, cloning, and live migration of running guests.
Applications
- Server consolidation, packing many Virtual Machines onto fewer physical hosts.
- Public and private Cloud Infrastructure offering elastic compute.
- Multi-Tenancy isolation between customers on shared hardware.
- Secure workload separation, complementing a Trusted Execution Environment.