(1) The name given to various programming language interpreters. See Java Virtual Machine and Python.
(2) One instance of an operating system along with one or more applications running in an isolated partition within the computer. It enables different operating systems to run in the same computer at the same time as well as prevents applications from interfering with each other. This differs from a dual-boot or multiboot environment, in which the user has to choose only one OS at startup (see dual-boot). All virtual machines run simultaneously.
Each virtual machine is like a "machine within the machine" and functions as if it owned the entire computer. The operating systems in each virtual machine partition are called "guest operating systems," and they communicate with the hardware via the virtual machine control program called a "virtual machine monitor" (VMM). The VMM "virtualizes" the hardware for each virtual machine.
Although a hot topic in the IT world, virtual machine technology dates back to the 1960s (see VM). The terms "virtual machine" and "virtualization" are used synonymously; however, virtualization also refers to other techniques (see virtualization).
The following illustration shows a simple comparison of three applications running in a regular computer versus a virtualized computer. In the VMM example, the guest operating systems may be the same or different. For more details about the VMM, see virtual machine monitor. See virtualization, application virtualization and OS virtualization.
Paravirtualization and Hardware
Guest operating systems can run in a virtual machine with or without modification. If changes are made to the OS to recognize the VMM, it is said to be "paravirtualized." For example, Linux and various Unix versions have been paravirtualized to run in the Xen VM environment. However, if the CPU hardware supports virtualization, Xen can run guest operating systems unmodified. In 2004 and 2006, Intel and AMD added virtualization to their CPUs, which traps the calls to the x86 hardware, making it easier to develop VMMs that run ordinary non-paravirtualized guest operating systems (see hardware virtualization).
Advantages of Virtualization
#1 - Consolidation
Multiple operating systems can run in the same server, eliminating the need to dedicate a single machine to one application. Old and new applications can run simultaneously with their respective operating systems in multicore servers with many threads of execution, saving space and power consumption in the datacenter. New versions of an OS and new applications can be deployed without purchasing new hardware.
#2 - Stability and Security
Conflicts can arise between supposedly stable applications, and troubleshooting can be daunting. As a result, cautious system administrators often host each type of application in a separate server even if the server is grossly underutilized. Multiple virtual machines running bread and butter applications are kept safely separated from each other. In addition, since each VM is isolated from the rest, a security breach in one does not affect the others. The fault tolerance and security brought about by the isolation of each virtual machine is a major benefit of virtualization.
#3 - Development Flexibility
A virtualized machine can host numerous versions of an operating system, allowing developers to test their programs in different OS environments on the same machine. In addition, with each application running in its own virtual partition, crashing in one virtual machine will not bring down the system.
#4 - Migration and Cloning
Virtual machines, each with their own OS and applications, function like self-contained packages that are said to be "decoupled from the hardware." It is relatively easy to move a VM from one server to another to balance the workload, to migrate to faster hardware, as well as to recover from hardware failure. VMs can also be quickly cloned and deployed.
#5 - Desktop Virtualization
An increasing trend is to store a user's desktop (OS and applications) in a separate virtual machine in the server and use the PC or a dedicated terminal as a "thin client" to the server. Each user is isolated from all other users, due to the virtual machine technology, and the maintenance of the applications is shifted from each user's office to the datacenter (see thin client). See virtual machine monitor, virtualization, application virtualization and OS virtualization.
(2) One instance of an operating system along with one or more applications running in an isolated partition within the computer. It enables different operating systems to run in the same computer at the same time as well as prevents applications from interfering with each other. This differs from a dual-boot or multiboot environment, in which the user has to choose only one OS at startup (see dual-boot). All virtual machines run simultaneously.
Each virtual machine is like a "machine within the machine" and functions as if it owned the entire computer. The operating systems in each virtual machine partition are called "guest operating systems," and they communicate with the hardware via the virtual machine control program called a "virtual machine monitor" (VMM). The VMM "virtualizes" the hardware for each virtual machine.
Although a hot topic in the IT world, virtual machine technology dates back to the 1960s (see VM). The terms "virtual machine" and "virtualization" are used synonymously; however, virtualization also refers to other techniques (see virtualization).
The following illustration shows a simple comparison of three applications running in a regular computer versus a virtualized computer. In the VMM example, the guest operating systems may be the same or different. For more details about the VMM, see virtual machine monitor. See virtualization, application virtualization and OS virtualization.
Paravirtualization and Hardware
Guest operating systems can run in a virtual machine with or without modification. If changes are made to the OS to recognize the VMM, it is said to be "paravirtualized." For example, Linux and various Unix versions have been paravirtualized to run in the Xen VM environment. However, if the CPU hardware supports virtualization, Xen can run guest operating systems unmodified. In 2004 and 2006, Intel and AMD added virtualization to their CPUs, which traps the calls to the x86 hardware, making it easier to develop VMMs that run ordinary non-paravirtualized guest operating systems (see hardware virtualization).
Advantages of Virtualization
#1 - Consolidation
Multiple operating systems can run in the same server, eliminating the need to dedicate a single machine to one application. Old and new applications can run simultaneously with their respective operating systems in multicore servers with many threads of execution, saving space and power consumption in the datacenter. New versions of an OS and new applications can be deployed without purchasing new hardware.
#2 - Stability and Security
Conflicts can arise between supposedly stable applications, and troubleshooting can be daunting. As a result, cautious system administrators often host each type of application in a separate server even if the server is grossly underutilized. Multiple virtual machines running bread and butter applications are kept safely separated from each other. In addition, since each VM is isolated from the rest, a security breach in one does not affect the others. The fault tolerance and security brought about by the isolation of each virtual machine is a major benefit of virtualization.
#3 - Development Flexibility
A virtualized machine can host numerous versions of an operating system, allowing developers to test their programs in different OS environments on the same machine. In addition, with each application running in its own virtual partition, crashing in one virtual machine will not bring down the system.
#4 - Migration and Cloning
Virtual machines, each with their own OS and applications, function like self-contained packages that are said to be "decoupled from the hardware." It is relatively easy to move a VM from one server to another to balance the workload, to migrate to faster hardware, as well as to recover from hardware failure. VMs can also be quickly cloned and deployed.
#5 - Desktop Virtualization
An increasing trend is to store a user's desktop (OS and applications) in a separate virtual machine in the server and use the PC or a dedicated terminal as a "thin client" to the server. Each user is isolated from all other users, due to the virtual machine technology, and the maintenance of the applications is shifted from each user's office to the datacenter (see thin client). See virtual machine monitor, virtualization, application virtualization and OS virtualization.
 | Reproduced with permission from Computer Desktop Encyclopedia. Copyright (c) 1981-2009 The Computer Language Company Inc. All rights reserved. |
Additional Resources
- Ballmer: So far, Windows 7 sales are "fantastic"
- RE: Ballmer: So far, Windows 7 sales are One report has at 4% market share the weekend of launch so im sure its past that already.Has Windows 7 marketshare eclipsed total OS X marketshare yet?Just wondering. :)MSFT: 1/2000 = $56. Today, $28.40Win 7 may not be the catastrophe the last...
- Discussion threads 2009-11-05
- TurboFTP Server 1.00.705 (Windows)
- TurboFTP Server supports virtual domains, which means you can set up multiple virtual domains on a physical host machine and provide different services on it. You can map any local folder path to a virtual server folder and assign individual users or groups access rights to folders within a domain's...
- Software downloads 2009-11-05
- Java Runtime Environment (JRE) 6 Update 17 (Windows)
- The Java Runtime Environment JRE provides the libraries, the Java Virtual Machine, and other components to run applets and applications written in the Java programming language. In addition, two key deployment technologies are part of the JRE: Java Plug-in, which enables applets to run in popular browsers; and Java Web...
- Software downloads 2009-11-04
- Power Solutions Article:Â Highly Available Virtualization with Microsoft Hyper-V and SCVMM 2008
- In virtualized environments, high availability can be critical to avoiding lost revenue, maintaining productivity, and protecting data from system failure. Combining Microsoft® Hyper-V™ technology with Microsoft System Center Virtual Machine Manager SCVMM 2008 on Dell™ platforms can help organizations create highly available virtualized systems while offering simplified management, dynamic performance,...
- White papers 2009-11-04
- JumpBox for the MySQL Relational Database 1.1.11 (Mac)
- MySQL is probably the most widely used relational databases around. It's used as an integral component in many JumpBoxes and is also useful to have available in an easy to use standalone version. This JumpBox includes MySQL 5 along with PHPMyAdmin setup and ready to run. It's a great tool...
- Software downloads 2009-10-30
- My Top Scary Technology Trends
- The Most Terrifying:Google.Kills good companies by handing out "freebies". VERY scary.Machines replacing humansI thought they were tools to enhance our experience on earth.The worst is when customer is an AI telephone. "I'm sorry, could you repeat your last phrase. I did not understand". I thought the buttons were bad enough.RE:...
- Discussion threads 2009-10-29
- ImageJ 1.43j (Mac)
- ImageJ is a public domain Java image processing program inspired by NIH Image for the Macintosh. It runs, either as an online applet or as a downloadable application, on any computer with a Java 1.1 or later virtual machine. It can display, edit, analyze, process, save and print 8-bit, 16-bit...
- Software downloads 2009-10-28
- Disk2vhd 1.21 (Windows)
- Disk2vhd is a utility that creates VHD (Virtual Hard Disk - Microsoft's Virtual Machine disk format) versions of physical disks for use in Microsoft Virtual PC or Microsoft Hyper-V virtual machines VMs. You can run Disk2vhd on a system that is online. Disk2vhd uses Windows' Volume Snapshot capability, introduced in...
- Software downloads 2009-10-27
- Star Walk for iPhone 3.1 (Mobile)
- Make Star Walk for iPhone your virtual stars gazing guide, and discover all stars, planets, and constellations. Star Walk for iPhone features picture of the day, for any doubt on how to use the digital compass, the time machine, location selection and to get in contact with us for any...
- Software downloads 2009-10-27
- Open Search Server 1.1r632 (Windows)
- Open Search Server OSS is a search engine software developed under the GPL v3 open source licence. Built using the best open source technologies available, Open Search Server is a stable, high-performance piece of software. It is both a modern search engine and a suite of high-powered full text search...
- Software downloads 2009-10-26
- Remote Desktop Manager 5.6.3.0 (Windows)
- Remote Desktop Manager is a small application used to manage all your remote connections and virtual machine. Add, edit, delete, shared, organize and find your remote connection quickly. Compatible with Microsoft Remote Desktop, Terminal Services, VNC, LogMeIn, Team Viewer, Ftp, SSH, Telnet Dameware, X Window VMWare, Virtual PC, PC Anywhere,...
- Software downloads 2009-10-25
- My 7 favorite Windows 7 features
- Today Windows 7 hits the GA or general availability milestone. That means that you'll be able to pick up a PC with the OS pre-installed on it, or pick up a disc from your favorite virtual or bricks-and-mortar outlet. To celebrate, here are my top 7 favorite Windows 7 features....
- Blog posts 2009-10-22
- Windows 7: An impressive upgrade
- Windows 7 review:Windows 7 review: 'New' OS is just Vista with small changesPerformance enhancements"We have already determined that W7 won't make your computer run any faster. And if you are upgrading from XP, it might run slightly slower, just as with Vista. ......But it's not really anything new. We hate...
- Discussion threads 2009-10-21
- DotFix NiceProtect 3.9 (Windows)
- NiceProtect means external protection for your applications. Protection mechanism contents modern technologies of polymorphism, metamorphism and Virtual Machine protection. In addition, your program code may be packed that will reduce common size of program without loss of its functionality. As a result you have nice protection system for your applications....
- Software downloads 2009-10-21
- Windows XP Mode Q and A
- 7/Vista incompatible "Drivers" on XP modeMy otherwise perfectly working HP printer, Logitech webcam, and an analog microphone failed to work with Vista since the hardware vendors won't provide updated drivers while the older ones resulted in BSODs. Can these be made to work by installing the drivers into XP...
- Discussion threads 2009-10-20
- Who's a candidate for Desktop Linux? Your Kids.
- "Hannah Montana Linux" may not be ready to give to your kids yet, but it's an idea that has legs. My partner in crime in the Frugal Tech Show, Ken Hess, who blogs over at Daniweb, recently published his list of Top 10...
- Blog posts 2009-10-20
- Windows 7 in action: a closer look at Windows XP Mode
- Now that's coolSo XP apps can be run directly on the desktop? Now that's cool :).How is this different than Virtual PC?Ed, I have XP running under MS Virtual PC 2007 on my Vista Business x64 machine. How is this different? I know that I had to supply...
- Discussion threads 2009-10-19
- Teradata unveils cloud strategy, answer for Oracle's Exadata machine
- Data warehousing giant Teradata is outlining its cloud computing strategy including an internal cloud service and a public offering via Amazon Web Services. In addition, Teradata is rolling out an appliance it claims will provide a big performance boost. The announcements, timed for Teradata's partner conference in...
- Blog posts 2009-10-19
- Virtual ][ 6.3.5 (Mac)
- Virtual ][ is an application that emulates the Apple ][ computer. Its main purpose is to enjoy, on your Macintosh computer, the nostalgic fun of the Apple ][. The main features are: Emulates the Apple ][, Apple ][+ and Apple //e; Supports USB game pad or joystick Save a...
- Software downloads 2009-10-17
- Report: Microsoft prepping now for next beta of Security Essentials
- I have been invitedThe e-mail contains a link to a survey, and they will select the beta testers from the respondents by November 1.An excerpt form the mail:''In the coming months we will be rolling out an ongoing beta program. As part of the Microsoft Security Essentials ongoing beta program,...
- Discussion threads 2009-10-15
Neighboring Terms
Premier Vendor Content Whitepapers, webcasts & resources from our Power Center Sponsors
SmartPlanet
- Thought-provoking progressive ideas on diverse topics that intersect with technology, business, and life, and matter to the world at large. Visit SmartPlanet
- More from IBM
-
- How to Drive Better Business Outcomes with Exceptional Web Experiences Download the eBook
- Driving Business Agility through SOA Connectivity & Integration Read the White Paper from IBM
- Linking Decisions and Information for Organizational Performance Read the Tom Davenport study
