Virtual machines

Virtual machines
Software: Haiku, Inc. and Red Hat, Inc. Screenshot: VulcanSphere · GPL · source
Name	Virtual machines
Developer	VMware, Inc.; Microsoft; Oracle Corporation; Red Hat, Inc.
Released	1970s
Operating system	Guest-dependent
Platform	x86; ARM; SPARC; POWER
License	Proprietary and open-source

Virtual machines are software emulations that present a complete computer system environment to one or more guest operating systems, enabling execution of unmodified software within isolated instances. Originating from research at institutions such as Stanford University and IBM, they reshaped computing by supporting time-sharing, consolidation, and portability across disparate hardware platforms. The technology underpins cloud services offered by providers including Amazon Web Services, Google Cloud Platform, and Microsoft Azure and is integral to enterprise operations at firms like Netflix and Airbnb.

Overview

Virtual machines emulate hardware and provide virtualized instances that behave like physical machines, enabling multiple operating systems to run concurrently on a single host such as servers from Dell Technologies or Hewlett Packard Enterprise. Early research projects at MIT and industrial systems at IBM during the 1960s and 1970s demonstrated isolation and multiplexing; subsequent commercialization by VMware, Inc. and product lines from Microsoft and Oracle Corporation drove widespread adoption. VM technology is central to architectures promoted by Red Hat, Inc. and standards bodies like the Open Virtualization Format community. Enterprises adopt VMs for workload consolidation, disaster recovery strategies used by Sun Microsystems customers, and for development pipelines in organizations such as Google LLC.

Architecture and Components

A virtual machine system typically comprises a hypervisor layer developed by vendors like VMware, Inc. or Citrix Systems, a guest operating system such as Windows NT or Ubuntu, virtual hardware devices modeled after industry standards produced by Intel Corporation and Advanced Micro Devices, and management tooling exemplified by vCenter and OpenStack. Core components include virtual CPUs mapped to physical cores on processors like Intel Xeon or ARM Cortex-A, virtual memory managed in coordination with Linux Kernel features, virtual I/O devices emulating ethernet adapters found in Broadcom NICs, and virtual storage presented as files or block devices managed by products from NetApp and EMC Corporation. Integration with orchestration platforms maintained by Kubernetes ecosystems and configuration systems by Ansible or Puppet enables lifecycle control and automated provisioning across data centers run by Equinix and cloud operators.

Types and Classification

Virtual machines can be classified into system virtual machines that provide complete OS environments and process virtual machines that support a single process runtime; examples include the Java Virtual Machine for process-level portability and full-system hypervisors from Xen Project for system-level isolation. Another axis distinguishes type 1 bare-metal hypervisors such as Hyper-V and KVM from type 2 hosted hypervisors like VMware Workstation and VirtualBox. Specialized forms include para-virtualization pioneered by the Xen Project community, hardware-assisted virtualization relying on Intel VT-x and AMD-V extensions, and container-like lightweight sandboxes promoted by Docker, Inc. though containers are not VMs strictly. Classification also reflects intended deployment: enterprise virtualization suites from VMware, Inc. contrast with research prototypes from University of Cambridge groups.

Use Cases and Applications

Virtual machines enable server consolidation in enterprises such as Facebook data centers, desktop virtualization for organizations deploying Citrix Systems solutions, and multi-tenant isolation in public clouds operated by Amazon Web Services and Microsoft Azure. They support legacy application preservation for customers of SAP SE, testing and CI pipelines in companies like GitHub, and academic research clusters at institutions such as University of California, Berkeley. VMs facilitate virtual appliances distributed by Red Hat, Inc. partners, network function virtualization used by telecommunications firms like AT&T, and security sandboxes for malware analysis by teams at Symantec and McAfee, LLC.

Performance and Resource Management

Performance considerations involve CPU scheduling, memory ballooning and overcommit strategies implemented in systems like KVM and Xen Project, I/O virtualization using techniques such as SR-IOV standardized by PCI-SIG, and storage optimizations leveraging deduplication from vendors like NetApp. Resource management tools such as vCenter and OpenStack employ policies for live migration—techniques used by hyperscalers including Google LLC—to balance loads across hosts. Hardware features from Intel Corporation and AMD reduce virtualization overhead, while NUMA-aware schedulers and huge page support in Linux Kernel minimize performance penalties for large-memory VMs.

Security and Isolation

Isolation properties derive from architecture choices in hypervisors developed by VMware, Inc., Microsoft, and the Xen Project; however, historical vulnerabilities disclosed by researchers at University of California, Santa Barbara and security firms like Trend Micro have shown escape paths when hypervisors or device emulation are flawed. Mitigations employ hardware roots of trust such as Trusted Platform Module modules, secure boot chains standardized by UEFI specifications, and formal policies enforced by orchestration systems used by OpenStack and Kubernetes operators. Multi-tenant deployments of cloud providers such as Amazon Web Services rely on isolation controls, access audits from firms like Deloitte, and continuous patching workflows followed by organizations such as Red Hat, Inc..

Implementation and Hypervisors

Hypervisor implementations span open-source projects like KVM integrated into the Linux Kernel, Xen Project supported by the Linux Foundation, and commercial systems from VMware, Inc. and Microsoft. Virtual machine monitors implement traps and emulation, paravirtual drivers standardized by communities including the QEMU project accelerate I/O, and management stacks such as vCenter and oVirt deliver enterprise features. Performance and feature sets often reflect collaborations between chip vendors like Intel Corporation and software communities including Linux Kernel maintainers and the OpenStack ecosystem.

Category:Virtualization