Virtual machine

A software system that presents an abstract computing environment in which programs execute. It may emulate a physical computer’s instruction set or provide a language-specific runtime.

Hypervisor: Software that creates and manages virtual machines by allocating physical computing resources. A hypervisor provides the layer that lets multiple machine-level virtual machines share one host.
Process virtual machine: A virtual machine that supports one program during its execution, typically through a language runtime. This is the program-level form of virtual machine, distinct from a virtualized whole computer.
Java virtual machine: The runtime environment that executes Java bytecode and other supported languages' bytecode. It is a prominent process virtual machine designed around portable bytecode.
Server consolidation: The practice of replacing multiple lightly used servers with fewer, more heavily utilized systems. Virtual machines made it practical to host many isolated server workloads on one physical machine.
Instruction set architecture: The defined instructions, registers, and data types that software can use on a processor. Machine-level virtual machines reproduce or expose an instruction set as their execution target.
System virtual machine: A virtual machine that provides a complete system environment for an operating system. This is the machine-level form, presenting virtual hardware to a guest operating system.
Common Language Runtime: The execution environment for managed code in Microsoft's .NET platform. It supplies a process virtual machine with services such as compilation, memory management, and type safety.
Live migration: The transfer of a running virtual machine between physical hosts with little service interruption. A virtual machine's abstract hardware boundary allows its execution state to move between hosts.
Binary translation: The conversion of machine-code instructions from one instruction set into another. Some virtual machines translate guest instructions to run them on different host hardware.
Emulator: Software that reproduces the behavior of one computer system on another. Emulation can imitate hardware without providing the resource-sharing and isolation typical of virtualization.

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