Virtualization

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.

Types of virtualization

Hardware

Main article: Hardware virtualization

Hardware virtualization or platform virtualization refers to the creation of a virtual machine 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 Mac OS X may host a virtual machine that looks like a computer with the Microsoft Windows operating system. Subsequently, Microsoft Windows-based software can be run on that virtual machine.

In hardware virtualization, the term host machine refers to the actual machine on which the virtualization takes place; the term guest machine, however, refers to the virtual machine. Likewise, the adjectives host and guest are used to help 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:

1. Full virtualization: Almost complete simulation of the actual hardware to allow software, which typically consists of a guest operating system, to run unmodified
2. 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.
3. Paravirtualization: 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 must not be mistaken with 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 must not be mistaken with an emulator. These two are defined similarly: Both are computer programs that imitate hardware, but their domain of use in language differs.

See also: Mobile Virtualization

Software

• Operating system-level virtualization, hosting of multiple virtualized environments within a single OS instance
• Application virtualization and Workspace virtualization, the hosting of individual applications in an environment separated from the underlying OS

Memory

• Memory virtualization, aggregating RAM resources from networked systems into a single memory pool
• Virtual memory, giving an application program the impression that it has contiguous working memory, isolating it from the underlying physical memory implementation

Storage

• Storage virtualization, the process of completely abstracting logical storage from physical storage
• Distributed file system

Data

• Data virtualization, the presentation of data as an abstract layer, independent of underlying database systems, structures and storage
• Database virtualization, the decoupling of the database layer, which lies between the storage and application layers within the application stack

Network

• Desktop virtualization, the concept of separating a desktop environment from its physical computer (and its associated operating system) and storing it on another machine across a network, such as a center server. Thin clients employ desktop virtualization.
• Network virtualization, creation of a virtualized network addressing space within or across network subnets

See also

• Timeline of virtualization development
• Emulation (computing)
• Computer simulation
• Numeronym (explains why V12N is an abbreviation for "virtualization")