virtual machine


Also found in: Dictionary, Thesaurus, Medical, Legal, Financial, Acronyms, Wikipedia.
Related to virtual machine: Java Virtual Machine

virtual machine

[′vər·chə·wəl mə′shēn]
(computer science)
A portion of a computer system or of a computer's time that is controlled by an operating system and functions as though it were a complete system, although in reality the computer is shared with other independent operating systems.

Virtual Machine

(operating system)
(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.

http://vmdev.gpl.ibm.com/.

["History of VM"(?), Melinda Varian, Princeton University].

virtual machine

(2)
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.

virtual machine

(3)
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.

virtual machine

(1) The name given to various language interpreters. See Java Virtual Machine and Python.

(2) A virtual machine (VM) is an operating system and one or more apps running in an isolated partition within the computer. Depending on the size of the hardware, any number of VMs can be running. The more CPU cores, the more simultaneity (see multicore).

Dating back to the 1960s, virtual machines (VMs) are widely used to run multiple instances of the same OS, each running a different set of applications. The separate instances prevent apps from interfering with one another after a crash, especially when testing new software. Virtual machines differ from dual-boot or multiboot, whereby the user has to choose only one OS at startup (see dual-boot).


Non-Virtual Versus Virtual
The OS in each VM is a "guest operating system" that communicates with the hardware via the VM monitor. The guest OS may be the same or different. "Virtualization" is commonplace today. See virtual machine monitor, virtualization and paravirtualization.





Advantages of Virtualization



#1 - Consolidation
Multiple operating systems can run in the same server, eliminating the need to dedicate a single machine to each OS. New OS versions can be deployed and tested without adding hardware. In the datacenter, multicore servers with many threads of execution save space and power.

#2 - Stability and Security
Troubleshooting can be daunting when conflicts arise in supposedly stable apps. Prior to virtualization, cautious system administrators hosted each type of application in a separate server even if grossly underutilized. However, VMs are isolated from each other, and a security breach in one does not affect the others.

#3 - Development Flexibility
A virtualized computer can host numerous versions of an operating system, allowing developers to test their programs in different OS environments on the same machine.

#4 - Migration and Cloning
Virtual machines function like self-contained packages that are said to be "decoupled from the hardware." It is relatively easy to move a VM instance from one server to another to balance the workload, migrate to faster hardware or to recover from hardware failure.

#5 - Desktop Virtualization
Another virtualization trend is storing a user's OS and apps in a VM in the server and use the PC as a "thin client" to that VM. Each user is isolated from all others, and maintenance is shifted from the user's computer to the datacenter (see thin client). See virtual machine monitor, virtualization, application virtualization and OS virtualization.
References in periodicals archive ?
File recovery software that worked on physical computers running Windows XP would not work on a Windows XP virtual machine. Once again, it is a good practice to test software to ensure it works in the virtualization platform selected if possible.
If a necessary application does not run under modern versions of Windows, for example, an older version of the operating system can be installed under a virtual machine and the application can be run through it.
From the analysis above we found that most of existing research does not consider user service satisfaction, priority of virtual machines and real-time of virtual machine allocation.
"An energy aware framework for virtual machine placement in cloud federated data centers," in Proc.
This physical server forms the public cloud environment, provides the virtual machine and controls its physical resources [15].
Improved functions of Hyper-V hot backup can serve well for any purposes and goals where virtual machines used for different types of tasks, especially in business, real-time management and scientific computing systems.
Where assume [[eta].sub.ij]=[PMD.sub.ij], the algorithm expects to deploy a component to the virtual machine with best performance aiming at minimizing execution time of the component.
The fundamentals of virtual server data protection include exploding backup windows, where a combination of high server consolidation and high virtual machine (VM) density concentrates data ownership to a small number of physical servers with most resources dedicated for production workloads; and unprotected virtual machine data, where the ease of deploying new VMs leads to a virtual machine sprawl, making it tedious and time consuming for administrators to keep track of new virtual machines and to ensure correct data protection.
This guide incorporates all the changes that have been made to the Java Virtual Machine since the second edition in 1999.
The virtual machine (VM) must be configured with the appropriate operating system(s) and include the required security tools for each lab exercise.
Red Hat Enterprise Virtualisation delivers an open virtualisation hypervisor with kernel-based virtual machine (KVM) and corresponding management tools for both server and desktop virtualisation deployments.

Full browser ?