Virtual machine
Virtual machine
A virtual machine (VM) is a software-based emulation of a physical computer system that runs an operating system and applications in an isolated environment. Virtual machines are typically created and managed by a hypervisor, which allocates physical hardware resources—such as CPU, memory, and storage—to one or more VMs. Each VM contains its own guest operating system and behaves as a separate computer, enabling multiple operating systems to run concurrently on a single physical host.
History
The concept of virtual machines dates back to the 1960s, when IBM developed the CP-40 and later CP/CMS systems, which allowed multiple users to run separate operating system instances on a single mainframe. In the 1990s, commercial hypervisors for x86 architecture appeared, notably VMware Workstation (1999), which popularized VMs on commodity hardware. Later, open‑source solutions such as Xen and KVM expanded the technology, and major cloud providers—Amazon Web Services, Microsoft Azure, Google Cloud—now rely heavily on VMs for IaaS.
Features
- Isolation: Each VM operates in a walled-off environment, preventing one VM’s failures or security breaches from affecting others.
- Hardware independence: VMs abstract the underlying hardware, allowing the same VM to run on different physical machines without modification.
- Snapshots and cloning: Users can capture the state of a VM at a point in time (snapshot) and replicate it (clone) for rapid deployment.
- Live migration: Modern hypervisors can move a running VM from one physical host to another with zero downtime.
Types
- System virtual machines (hardware VMs): These provide a complete platform capable of running a full operating system. Examples include VMs created by VMware vSphere, Microsoft Hyper‑V, and KVM.
- Process virtual machines: These run as a single application and support a single process, typically for platform independence (e.g., the Java Virtual Machine, .NET Common Language Runtime).
Uses
Virtual machines are widely used for server consolidation, software testing, development environments, legacy application migration, and cloud computing. They enable efficient use of hardware resources by allowing multiple virtual servers on one physical machine, reduce energy costs, and simplify disaster recovery through rapid provisioning and failover.