Virtualization is simply the logical separation of the request for some service from the physical resources that actually provide that service. In practical terms, virtualization provides the ability to run applications, operating systems, or system services in a logically distinct system environment that is independent of a specific physical computer system. Obviously, all of these have to be running on a certain computer system at any given time, but virtualization provides a level of logical abstraction that liberates applications, system services, and even the operating system that supports them from being tied to a specific piece of hardware. Virtualization’s focus on logical operating environments rather than physical ones makes applications, services, and instances of an operating system portable across different physical computer systems.
The classic example of virtualization that most people are already familiar with is virtual memory, which enables a computer system to appear to have more memory than is physically installed on that system. Virtual memory is a memory-management technique that enables an operating system to see and use noncontiguous segments of memory as a single, contiguous memory space. Virtual memory is traditionally implemented in an operating system by paging, which enables the operating system to use a file or dedicated portion of some storage device to save pages of memory that are not actively in use.
Known as a “paging file” or “swap space,” the system can quickly transfer pages of memory to and from this area as the operating system or running applications require access to the contents of those pages. Modern operating systems such as UNIX-like operating systems (including Linux, the *BSD operating systems, and Mac OS X) and Microsoft Windows all use some form of virtual memory to enable the operating system and applications to access more data than would fit into physical memory.
Taken from : William Von Hagen "Professional Xen Virtualization" 2008The classic example of virtualization that most people are already familiar with is virtual memory, which enables a computer system to appear to have more memory than is physically installed on that system. Virtual memory is a memory-management technique that enables an operating system to see and use noncontiguous segments of memory as a single, contiguous memory space. Virtual memory is traditionally implemented in an operating system by paging, which enables the operating system to use a file or dedicated portion of some storage device to save pages of memory that are not actively in use.
Known as a “paging file” or “swap space,” the system can quickly transfer pages of memory to and from this area as the operating system or running applications require access to the contents of those pages. Modern operating systems such as UNIX-like operating systems (including Linux, the *BSD operating systems, and Mac OS X) and Microsoft Windows all use some form of virtual memory to enable the operating system and applications to access more data than would fit into physical memory.
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