Virtualization
Encyclopedia
Virtualization, in computing, is the creation of a virtual (rather than actual) version of something, such as a hardware platform, operating system, a storage device or network resources.
Virtualization can be viewed as part of an overall trend in enterprise IT that includes autonomic computing
, a scenario in which the IT environment will be able to manage itself based on perceived activity, and utility computing, in which computer processing power is seen as a utility that clients can pay for only as needed. The usual goal of virtualization is to centralize administrative tasks while improving scalability and work loads.
that acts like a real computer with an operating system. Software executed on these virtual machines is separated from the underlying hardware resources. For example, a computer that is running Microsoft Windows
may host a virtual machine that looks like a computer with Ubuntu Linux operating system; Ubuntu-based software can be run on the virtual machine.
In hardware virtualization, the host machine is the actual machine on which the virtualization takes place, and the guest machine is the virtual machine. The words host and guest are used to distinguish the software that runs on the actual machine from the software that runs on the virtual machine. The software or firmware that creates a virtual machine on the host hardware is called a hypervisor
or Virtual Machine Monitor.
Different types of hardware virtualization include:
Hardware-assisted virtualization is a way of improving the efficiency of hardware virtualization. It involves employing specially-designed CPUs and hardware components that help improve the performance of a guest environment.
Hardware virtualization is not the same as hardware emulation
: in hardware emulation, a piece of hardware imitates another, while in hardware virtualization, a hypervisor (a piece of software) imitates a particular piece of computer hardware or the whole computer altogether. Furthermore, a hypervisor is not the same as an emulator
; both are computer programs that imitate hardware, but their domain of use in language differs.
from the physical machine.
One form of desktop virtualization, virtual desktop infrastructure (VDI), can be thought as a more advanced form of hardware virtualization: Instead of directly interacting with a host computer via a keyboard, mouse and monitor connected to it, the user interacts with the host computer over a network connection (such as a LAN
, Wireless LAN
or even the Internet
) using another desktop computer or a mobile device. In addition, the host computer in this scenario becomes a server computer capable of hosting multiple virtual machines at the same time for multiple users.
Another form, session virtualization, allows multiple users to connect and log into
a shared but powerful computer over the network and use it simultaneously. Each is given a desktop and a personal folder in which they store their files.
Thin client
s, which are seen in desktop virtualization, are simple and/or cheap computers that are primarily designed to connect to the network; they may lack significant hard disk storage space, RAM or even processing power
.
Virtualization
Virtualization can be viewed as part of an overall trend in enterprise IT that includes autonomic computing
Autonomic Computing
Autonomic Computing refers to the self-managing characteristics of distributed computing resources, adapting to unpredictable changes whilst hiding intrinsic complexity to operators and users...
, a scenario in which the IT environment will be able to manage itself based on perceived activity, and utility computing, in which computer processing power is seen as a utility that clients can pay for only as needed. The usual goal of virtualization is to centralize administrative tasks while improving scalability and work loads.
Hardware
Hardware virtualization or platform virtualization refers to the creation of a virtual machineVirtual machine
A virtual machine is a "completely isolated guest operating system installation within a normal host operating system". Modern virtual machines are implemented with either software emulation or hardware virtualization or both together.-VM Definitions:A virtual machine is a software...
that acts like a real computer with an operating system. Software executed on these virtual machines is separated from the underlying hardware resources. For example, a computer that is running Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
may host a virtual machine that looks like a computer with Ubuntu Linux operating system; Ubuntu-based software can be run on the virtual machine.
In hardware virtualization, the host machine is the actual machine on which the virtualization takes place, and the guest machine is the virtual machine. The words host and guest are used to distinguish the software that runs on the actual machine from the software that runs on the virtual machine. The software or firmware that creates a virtual machine on the host hardware is called a hypervisor
Hypervisor
In computing, a hypervisor, also called virtual machine manager , is one of many hardware virtualization techniques that allow multiple operating systems, termed guests, to run concurrently on a host computer. It is so named because it is conceptually one level higher than a supervisory program...
or Virtual Machine Monitor.
Different types of hardware virtualization include:
- Full virtualizationFull virtualizationIn computer science, full virtualization is a virtualization technique used to provide a certain kind of virtual machine environment, namely, one that is a complete simulation of the underlying hardware...
: Almost complete simulation of the actual hardware to allow software, which typically consists of a guest operating system, to run unmodified - Partial virtualization: Some but not all of the target environment is simulated. Some guest programs, therefore, may need modifications to run in this virtual environment.
- ParavirtualizationParavirtualizationIn computing, paravirtualization is a virtualization technique that presents a software interface to virtual machines that is similar but not identical to that of the underlying hardware....
: A hardware environment is not simulated; however, the guest programs are executed in their own isolated domains, as if they are running on a separate system. Guest programs need to be specifically modified to run in this environment.
Hardware-assisted virtualization is a way of improving the efficiency of hardware virtualization. It involves employing specially-designed CPUs and hardware components that help improve the performance of a guest environment.
Hardware virtualization is not the same as hardware emulation
Hardware emulation
In integrated circuit design, hardware emulation is the process of imitating the behavior of one or more pieces of hardware with another piece of hardware, typically a special purpose emulation system. The emulation model is usually based on RTL source code, which is compiled into the format...
: in hardware emulation, a piece of hardware imitates another, while in hardware virtualization, a hypervisor (a piece of software) imitates a particular piece of computer hardware or the whole computer altogether. Furthermore, a hypervisor is not the same as an emulator
Emulator
In computing, an emulator is hardware or software or both that duplicates the functions of a first computer system in a different second computer system, so that the behavior of the second system closely resembles the behavior of the first system...
; both are computer programs that imitate hardware, but their domain of use in language differs.
Desktop
Desktop virtualization is the concept of separating the logical desktopDesktop environment
In graphical computing, a desktop environment commonly refers to a style of graphical user interface derived from the desktop metaphor that is seen on most modern personal computers. These GUIs help the user in easily accessing, configuring, and modifying many important and frequently accessed...
from the physical machine.
One form of desktop virtualization, virtual desktop infrastructure (VDI), can be thought as a more advanced form of hardware virtualization: Instead of directly interacting with a host computer via a keyboard, mouse and monitor connected to it, the user interacts with the host computer over a network connection (such as a LAN
Län
Län and lääni refer to the administrative divisions used in Sweden and previously in Finland. The provinces of Finland were abolished on January 1, 2010....
, Wireless LAN
Wireless LAN
A wireless local area network links two or more devices using some wireless distribution method , and usually providing a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network...
or even the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
) using another desktop computer or a mobile device. In addition, the host computer in this scenario becomes a server computer capable of hosting multiple virtual machines at the same time for multiple users.
Another form, session virtualization, allows multiple users to connect and log into
Login
Login is the method whereby a user obtains access to a computer system.Login may also refer to:*Magazines:** LOGiN, published by Enterbrain** ;login:, published by USENIX* Login, Carmarthenshire, an hamlet in Carmarthenshire...
a shared but powerful computer over the network and use it simultaneously. Each is given a desktop and a personal folder in which they store their files.
Thin client
Thin client
A thin client is a computer or a computer program which depends heavily on some other computer to fulfill its traditional computational roles. This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself...
s, which are seen in desktop virtualization, are simple and/or cheap computers that are primarily designed to connect to the network; they may lack significant hard disk storage space, RAM or even processing power
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
.
Software
- Operating system-level virtualizationOperating system-level virtualizationOperating system-level virtualization is a server virtualization method where the kernel of an operating system allows for multiple isolated user-space instances, instead of just one. Such instances may look and feel like a real server, from the point of view of its owner...
, hosting of multiple virtualized environments within a single OS instance - Application virtualizationApplication VirtualizationApplication virtualization is an umbrella term that describes software technologies that improve portability, manageability and compatibility of applications by encapsulating them from the underlying operating system on which they are executed. A fully virtualized application is not installed in...
and workspace virtualizationWorkspace virtualizationWorkspace virtualization is a way of distributing applications to client computers using application virtualization however it also bundles several applications together into one complete workspace. It is an approach that encapsulates and isolates an entire computing workspace...
, the hosting of individual applications in an environment separated from the underlying OS. Application virtualization is closely associated with the concept of portable applicationPortable applicationA portable application , sometimes also called standalone, is a computer software program designed to run independently from an operating system...
s.
Memory
- Memory virtualizationMemory virtualizationIn computer science, memory virtualization decouples volatile random access memory resources from individual systems in the data center, and then aggregates those resources into a virtualized memory pool available to any computer in the cluster. The memory pool is accessed by the operating system...
, aggregating RAM resources from networked systems into a single memory pool - Virtual memoryVirtual memoryIn computing, virtual memory is a memory management technique developed for multitasking kernels. This technique virtualizes a computer architecture's various forms of computer data storage , allowing a program to be designed as though there is only one kind of memory, "virtual" memory, which...
, giving an application program the impression that it has contiguous working memory, isolating it from the underlying physical memory implementation
Storage
- Storage virtualizationStorage VirtualizationStorage virtualization or storage virtualisation is a concept and term used within computer science. Specifically, storage systems may use virtualization concepts as a tool to enable better functionality and more advanced features within the storage system.Broadly speaking, a 'storage system' is...
, the process of completely abstracting logical storage from physical storage - Distributed file systemDistributed file systemNetwork file system may refer to:* A distributed file system, which is accessed over a computer network* Network File System , a specific brand of distributed file system...
- Storage hypervisorStorage hypervisorIn computing, a storage hypervisor is a portable software program that runs on a physical hardware platform, on a virtual machine, inside a hypervisor OS or in all three places. It may co-reside with virtual machine supervisors or have exclusive control of its platform...
Data
- Data virtualizationData virtualizationData virtualization describes the process of abstracting disparate data sources through a single data access layer ....
, the presentation of data as an abstract layer, independent of underlying database systems, structures and storage - Database virtualizationDatabase VirtualizationDatabase virtualization is the decoupling of the database layer, which lies between the storage and application layers within the application stack...
, the decoupling of the database layer, which lies between the storage and application layers within the application stack
Network
- Network virtualizationNetwork virtualizationIn computing, Network Virtualization is the process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network...
, creation of a virtualized network addressing space within or across network subnets
See also
- Timeline of virtualization development
- Emulation (computing)
- Computer simulationComputer simulationA computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...
- NumeronymNumeronymA numeronym is a number-based word.Most commonly, a numeronym is a word where a number is used to form an abbreviation . Pronouncing the letters and numbers may sound similar to the full word: "K9" for "canine"...
(explains why "V12N" is an abbreviation for "virtualization")
Virtualization