Introduction

Introduction
Virtualization in a literal sense means something which is not real, something which does not has any physical existence. In computer science the earliest encounter with this idea can be thought in terms of virtual memory, the computer system is deceived into thinking that it has more physical memory at its disposal than actually is. A more befitting definition related to computer science is “it is an abstraction of physical resources for interacting applications”. Here application can be a computer system as well as any process. Computer operating systems are developed on assumption that only a single instance will run on a single machine. Virtualization breaks this mapping and allows division of physical resources to create separate virtual computer systems within a single machine.Thus multiple instances of operating system can run on a single machine.
The commercial application of this idea was implemented by IBM in 1960’s when it developed 370 series which allowed its mainframes to run multiple operating systems simultaneously. The greatest benefit was time sharing of expensive hardware. In 1990’s with the introduction of low cost hardware and multitasking operating systems, organizations lost interest in the technology. Although during this period VM/386 and hardware support (V8086 mode) existed but was not popular.
In late 1990’s the technology re-emerged. The main reason for this was that cost incurred in managing computer servers involved their maintenance, support and costs associated with system breaches and failures. Virtualization provided with the solution, Server consolidation which allowed many virtual servers to run on less number of machines with benefits like load balancing and failure management. Today, commercial virtualization products by VMware and Microsoft are widely used, with millions of copies having been sold. In addition to their use in server environments, these virtual machine technologies also are used in desktop environments to run multiple operating systems, typically Windows and Linux.
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