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Hardware virtualization is the virtualization of computers as complete hardware platforms, certain logical abstractions of their componentry, or only the functionality required to run various operating systems. Virtualization hides the physical characteristics of a computing platform from the users, presenting instead an abstract computing platform.[1][2] At its origins, the software that controlled virtualization was called a "control program", but the terms "hypervisor" or "virtual machine monitor" became preferred over time.[3]


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The term "virtualization" was coined in the 1960s to refer to a virtual machine (sometimes called "pseudo machine"), a term which itself dates from the experimental IBM M44/44X system.[3] The creation and management of virtual machines has also been called "platform virtualization", or "server virtualization", more recently.[4][5]

Platform virtualization is performed on a given hardware platform by host software (a control program), which creates a simulated computer environment, a virtual machine (VM), for its guest software. The guest software is not limited to user applications; many hosts allow the execution of complete operating systems. The guest software executes as if it were running directly on the physical hardware, with several notable caveats. Access to physical system resources (such as the network access, display, keyboard, and disk storage) is generally managed at a more restrictive level than the host processor and system-memory. Guests are often restricted from accessing specific peripheral devices, or may be limited to a subset of the device's native capabilities, depending on the hardware access policy implemented by the virtualization host.[citation needed]

Virtualization often exacts performance penalties, both in resources required to run the hypervisor, and as well as in reduced performance on the virtual machine compared to running native on the physical machine.[citation needed]

Reasons for virtualization

However, when multiple VMs are concurrently running on the same physical host, each VM may exhibit varying and unstable performance which highly depends on the workload imposed on the system by other VMs. This issue can be addressed by appropriate installation techniques for temporal isolation among virtual machines.

There are several approaches to platform virtualization.

Examples of virtualization use cases:

Full virtualization

Main article: Full virtualization

Logical diagram of full virtualization.

In full virtualization, the virtual machine simulates enough hardware to allow an unmodified "guest" OS designed for the same instruction set to be run in isolation. This approach was pioneered in 1966 with the IBM CP-40 and CP-67, predecessors of the VM family.

Hardware-assisted virtualization

Main article: Hardware-assisted virtualization

In hardware-assisted virtualization, the hardware provides architectural support that facilitates building a virtual machine monitor and allows guest OSs to be run in isolation.[10] Hardware-assisted virtualization was first introduced on the IBM System/370 in 1972, for use with VM/370, the first virtual machine operating system.

In 2005 and 2006, Intel and AMD developed additional hardware to support virtualization ran on their platforms. Sun Microsystems (now Oracle Corporation) added similar features in their UltraSPARC T-Series processors in 2005.

In 2006, first-generation 32- and 64-bit x86 hardware support was found to rarely offer performance advantages over software virtualization.[11]


Main article: Paravirtualization

In paravirtualization, the virtual machine does not necessarily simulate hardware, but instead (or in addition) offers a special API that can only be used by modifying[clarification needed] the "guest" OS. For this to be possible, the "guest" OS's source code must be available. If the source code is available, it is sufficient to replace sensitive instructions with calls to VMM APIs (e.g.: "cli" with "vm_handle_cli()"), then re-compile the OS and use the new binaries. This system call to the hypervisor is called a "hypercall" in TRANGO and Xen; it is implemented via a DIAG ("diagnose") hardware instruction in IBM's CMS under VM[clarification needed] (which was the origin of the term hypervisor)..

Operating-system-level virtualization

Main article: OS-level virtualization

In operating-system-level virtualization, a physical server is virtualized at the operating system level, enabling multiple isolated and secure virtualized servers to run on a single physical server. The "guest" operating system environments share the same running instance of the operating system as the host system. Thus, the same operating system kernel is also used to implement the "guest" environments, and applications running in a given "guest" environment view it as a stand-alone system.

Hardware virtualization disaster recovery

A disaster recovery (DR) plan is often considered good practice for a hardware virtualization platform. DR of a virtualization environment can ensure high rate of availability during a wide range of situations that disrupt normal business operations. In situations where continued operations of hardware virtualization platforms is important, a disaster recovery plan can ensure hardware performance and maintenance requirements are met. A hardware virtualization disaster recovery plan involves both hardware and software protection by various methods, including those described below.[12][13]

Tape backup for software data long-term archival needs
This common method can be used to store data offsite, but data recovery can be a difficult and lengthy process. Tape backup data is only as good as the latest copy stored. Tape backup methods will require a backup device and ongoing storage material.
Whole-file and application replication
The implementation of this method will require control software and storage capacity for application and data file storage replication typically on the same site. The data is replicated on a different disk partition or separate disk device and can be a scheduled activity for most servers and is implemented more for database-type applications.
Hardware and software redundancy
This method ensures the highest level of disaster recovery protection for a hardware virtualization solution, by providing duplicate hardware and software replication in two distinct geographic areas.[14]

See also


  1. ^ Turban, E; King, D.; Lee, J.; Viehland, D. (2008). "19". Electronic Commerce A Managerial Perspective (PDF) (5th ed.). Prentice-Hall. p. 27.
  2. ^ "Virtualization in education" (PDF). IBM. October 2007. Retrieved 6 July 2010.
  3. ^ a b Creasy, R.J. (1981). "The Origin of the VM/370 Time-sharing System" (PDF). IBM. Retrieved 26 February 2013.
  4. ^ Software, Performance (23 May 2018). "Virtual Machines: An Introduction to Platform Virtualization". Performance Software. Retrieved 8 July 2023.
  5. ^ "What is Server Virtualization?".
  6. ^ "Chip Aging Accelerates". 14 February 2018.
  7. ^ [1] Profiling Energy Usage for Efficient Consumption; Rajesh Chheda, Dan Shookowsky, Steve Stefanovich, and Joe Toscano
  8. ^ VMware server consolidation overview
  9. ^ Examining VMware Archived 22 November 2019 at the Wayback Machine Dr. Dobb's Journal August 2000 By Jason Nieh and Ozgur Can Leonard
  10. ^ Uhlig, R. et al.; "Intel virtualization technology," Computer , vol.38, no.5, pp. 48-56, May 2005
  11. ^ A Comparison of Software and Hardware Techniques for x86 Virtualization, Keith Adams and Ole Agesen, VMware, ASPLOS’06 21–25 October 2006, San Jose, California, USA "Surprisingly, we find that the first-generation hardware support rarely offers performance advantages over existing software techniques. We ascribe this situation to high VMM/guest transition costs and a rigid programming model that leaves little room for software flexibility in managing either the frequency or cost of these transitions."
  12. ^ "The One Essential Guide to Disaster Recovery: How to Ensure IT and Business Continuity" (PDF). Vision Solutions, Inc. 2010. Archived from the original (PDF) on 16 May 2011.
  13. ^ Wold, G (2008). "Disaster Recovery Planning Process". Archived from the original on 15 August 2012.
  14. ^ "Disaster Recovery Virtualization Protecting Production Systems Using VMware Virtual Infrastructure and Double-Take" (PDF). VMware. 2010. Archived from the original (PDF) on 23 September 2010.