Virtual Machine
Virtual machine techniques enable several operating systems ("guest" operating systems) or other software to run on the same computer so that each thinks it has a whole computer to itself, and each of these simulated whole computers is called a "virtual machine". The operating system which really controls the computer is usually called a hypervisor. Two of the major components of the hypervisor are:
- Virtual memory management. Each virtual machine appears to have a complete range of addresses from 0 to some large number, and virtual memory techniques prevent different virtual machines from confusing each other.
- Simulating "privileged" functions on behalf of the "guest" operating systems. "Privileged" functions are those which enable programs to take over all or at least large parts of the computer, and usually operating systems immediately terminate any other program which tries to use them. But "guest" operating systems think they are entitled to use these functions, so the hypervisor detects their attempts to do so and runs the privileged functions on their behalf, using virtual memory techniques to prevent them from corrupting memory areas used by other "guest" operating systems.
Read more about this topic: History Of IBM Mainframe Operating Systems, Technical Notes
Famous quotes containing the words virtual and/or machine:
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