History of IBM Mainframe Operating Systems - Technical Notes - Virtual Machine

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

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Famous quotes containing the words machine and/or virtual:

    The machine is impersonal, it takes the pride away from a piece of work, the individual merits and defects that go along with all work that is not done by a machine—which is to say, its little bit of humanity.
    Friedrich Nietzsche (1844–1900)

    Tragedy dramatizes human life as potentiality and fulfillment. Its virtual future, or Destiny, is therefore quite different from that created in comedy. Comic Destiny is Fortune—what the world will bring, and the man will take or miss, encounter or escape; tragic Destiny is what the man brings, and the world will demand of him. That is his Fate.
    Susanne K. Langer (1895–1985)