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 intermediatelanguage) 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, PortableStandard Lisp, Parallel Virtual Machine, Sequential ParlogMachine, 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 operatingsystem 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use of VM is the running of both outdated and current versions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)