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Define the word virtual machine

virtual machine
     
        1. An abstract machine for which an interpreter exists.
        Virtual machines are often used in the implementation of
        portable executors for high-level languages.  The HLL is
        compiled into code for the virtual machine (an intermediate language) which is then executed by an interpreter written
        in assembly language or some other portable language like
        C.
     
        Examples are Core War, Java Virtual Machine, OCODE,
        OS/2, POPLOG, Portable Scheme Interpreter, Portable Standard Lisp, Parallel Virtual Machine, Sequential Parlog Machine, SNOBOL Implementation Language, SODA,
        Smalltalk.
     
        2. A software emulation of a physical computing environment.
     
        The term gave rise to the name of IBM's VM operating system whose task is to provide one or more simultaneous
        execution environments in which operating systems or other
        programs may execute as though they were running "on the bare
        iron", that is, without an eveloping Control Program.  A major
        use of VM is the running of both outdated and current versions
        of the same operating system on a single CPU complex for the
        purpose of system migration, thereby obviating the need for a
        second processor.
     
        (2002-04-15)
     
     

Virtual Machine
     
         (VM) An IBM pseudo-operating system
        hypervisor running on IBM 370, ESA and IBM 390
        architecture computers.
     
        VM comprises CP (Control Program) and CMS (Conversational Monitor System) providing Hypervisor and personal computing
        environments respectively.  VM became most used in the early
        1980s as a Hypervisor for multiple DOS/VS and DOS/VSE
        systems and as IBM's internal operating system of choice.  It
        declined rapidly following widespread adoption of the IBM PC
        and hardware partitioning in microcode on IBM mainframes
        after the IBM 3090.
     
        VM has been known as VM/SP (System Product, the successor to
        CP/67), VM/XA, and currently as VM/ESA (Enterprise Systems
        Architecture).  VM/ESA is still in used in 1999, featuring a
        web interface, Java, and DB2.  It is still a major IBM
        operating system.
     
        Home (http://vmdev.gpl.ibm.com/).
     
        ["History of VM"(?), Melinda Varian, Princeton University].
     
        (1999-10-31)