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In virtualization, input/output virtualization (I/O virtualization) is a methodology to simplify management, lower costs and improve performance of servers in enterprise environments. I/O virtualization environments are created by abstracting the upper layer protocols from the physical connections .
Full virtualization requires that every salient feature of the hardware be reflected into one of several virtual machines – including the full instruction set, input/output operations, interrupts, memory access, and whatever other elements are used by the software that runs on the bare machine, and that is intended to run in a virtual machine.
Application virtualization also enables simplified operating system migrations. [4] Applications can be transferred to removable media or between computers without the need of installing them, becoming portable software. Application virtualization uses fewer resources than a separate virtual machine.
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 emulates the hardware environment of its host architecture, allowing multiple OSes to run unmodified and in isolation.
In both storage and server virtualization, the applications are unaware that the resources they are using are virtual rather than physical, so efficiency and flexibility are achieved without application changes. In the same way, memory virtualization allocates the memory of an entire networked cluster of servers among the computers in that cluster.
The virtualization software or device uses the metadata to re-direct I/O requests. It will receive an incoming I/O request containing information about the location of the data in terms of the logical disk (vdisk) and translates this into a new I/O request to the physical disk location. For example, the virtualization device may :
However, local desktop virtualization implementations do not always allow applications developed for one system architecture to run on another. For example, it is possible to use local desktop virtualization to run Windows 7 on top of OS X on an Intel-based Apple Mac, using a hypervisor, as both use the same x86 architecture.
x86 virtualization is the use of hardware-assisted virtualization capabilities on an x86/x86-64 CPU.. In the late 1990s x86 virtualization was achieved by complex software techniques, necessary to compensate for the processor's lack of hardware-assisted virtualization capabilities while attaining reasonable performance.