plna virtualizace: simulaci kompletniho hardware se vytvari virtualni stroj, na nemz bezi hostovany system. Hostovany system tedy nepotrebuje zadne upravy a lze takto dokonce provozovat systemy urcene pro jinou architekturu nez je fyzicka. Nevyhodou je velka rezie. (napr. VMware, VirtualPC, qemu)

nativni virtualizace: virtualni stroj simuluje pouze minimalni cast hw, ke zbytku pristupuji hostovane systemy primo. Jejich vzajemna izolace je zajistena vytvorenim barier mezi domenami. Hostovane system opet nevyzaduji zadne upravy, musi vsak jiz odpovidat architekture fyzickeho stroje. (napr. Virtuozo, vservers, zones)

paravirtualizace: spojuje lepsi z predchozich pristupu. Virtualni stroj se nesnazi hw simulovat, poskytuje hostovanemu prostredi specialni rozhrani pres ktere mu umozni k hw pristupovat. Hostovane systemy je treba upravit, tak aby toto rozhrani dokazali vyuzivat. Je to sice komplikovanejsi reseni, ale prinasi velmi dobry vykon, na rezii padne vykon v radu nekolika jednotek % (napr. uml, xen)



http://en.wikipedia.org/wiki/Virtualization
Virtualization
From Wikipedia, the free encyclopedia

In computing, virtualization is the process of presenting a logical grouping or subset of computing resources so that they can be accessed in ways that give benefits over the original configuration. This new virtual view of the resources is not restricted by the implementation, geographic location or the physical configuration of underlying resources. Commonly virtualized resources include computing power and data storage.

A good example of virtualization is modern symmetric multiprocessing computer architectures that contain more than one CPU. Operating systems are usually configured in such a way that the multiple CPUs can be presented as a single processing unit. Thus software applications can be written for a single logical (virtual) processing unit, which is much simpler than having to work with a large number of different processor configurations.

A new trend in virtualization is the concept of a virtualization engine which gives an overall holistic view of the entire network infrastructure.

Virtualization is a broad term that refers to the abstraction of resources across many aspects of computing. Some common applications of virtualization are listed below.

* A virtual machine is an environment which appears to a "guest" operating system as hardware, but is simulated in a contained software environment by the host system. The simulation must be robust enough for hardware drivers in the guest system to work. With paravirtualization, the virtual machine does not simulate hardware but instead offers a special API.
* Operating System-level Virtualization is virtualizing a physical server at the operating system level, enabling multiple isolated and secure virtualized servers on a single physical server.
* Partitioning is the splitting of a single, usually large, resource (such as disk space or network bandwidth) into a number of smaller, more easily utilized resources of the same type. This is sometimes also called "zoning," especially in storage networks.
* Aggregation, spanning, or concatenation all combine multiple resources into larger resources or resource pools. For example, symmetric multiprocessing combines many processors; RAID and volume managers combine many disks into one large logical disk; RAIN and network equipment uses multiple links combined to work as though they offered a single, higher-bandwidth link. At a meta-level, computer clusters do all of this.


See also

* Comparison of virtual machines
* Emulation
* Hypervisor
* Operating System-level Virtualization
* Virtualization software:
o Bochs
o Linux-VServer
o Microsoft Virtual PC
o Microsoft Virtual Server
o QEMU
o TRANGO
o Virtuozzo
o VMware Workstation, GSX Server, ESX Server
o IBM SAN Volume Controller
o Xen
o Parallels
* Virtualization hardware:
o AMD under the Pacifica technology specification.
o Intel under the 'Silvervale' virtualization technology.
* Virtualization Technology
* X86 virtualization

http://www.cl.cam.ac.uk/Research/SRG/netos/xen/

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zaujimavy virtualizacny soft Parallels Desktop