Application virtualization

Application virtualization is an umbrella term that describes software technologies that improve portability, manageability and compatibility of applications by encapsulating them from the underlying operating system on which they are executed. A fully virtualized application is not installed in the traditional sense^[1], although it is still executed as if it were. The application is fooled at runtime into believing that it is directly interfacing with the original operating system and all the resources managed by it, when in reality it is not. In this context, the term "virtualization" refers to the artifact being encapsulated (application), which is quite different to its meaning in hardware virtualization, where it refers to the artifact being abstracted (physical hardware).

1 Description
2 Related Technologies
3 Benefits of application virtualization
4 Limitations of application virtualization
5 See also
6 References

Description

Limited application virtualization is used in modern operating systems such a Microsoft Windows and Linux. For example, INI file mappings were introduced with Windows NT to virtualize, into the registry, the legacy INI files of applications originally written for Windows 3.1.^[2] Similarly, Windows Vista implements a shim that applies limited file and registry virtualization so that legacy applications that try to save user data in a readonly system location that was writable by anyone in early Windows, can still work.^[3]

Full application virtualization requires a virtualization layer.^[4] Application virtualization layers replace part of the runtime environment normally provided by the operating system. The layer intercepts all file and Registry operations of virtualized applications and transparently redirects them to a virtualized location, often a single file.^[5] The application never knows that it's accessing a virtual resource instead of a physical one. Since the application is now working with one file instead of many files and registry entries spread throughout the system, it becomes easy to run the application on a different computer and previously incompatible applications can be run side-by-side. Examples of this technology for the Windows platform are AppZero, BoxedApp, Cameyo, Ceedo, Evalaze, InstallFree, Citrix XenApp, Novell ZENworks Application VIrtualization, Endeavors Technologies Application Jukebox, Microsoft Application Virtualization, Software Virtualization Solution, Spoon (former Xenocode), VMware ThinApp and P-apps.

Related Technologies

Technology categories that fall under application virtualization include:

Application Streaming. Pieces of the application's code, data, and settings are delivered when they're first needed, instead of the entire application being delivered before startup. Running the packaged application may require the installation of a lightweight client application. Packages are usually delivered over a protocol such as HTTP, CIFS or RTSP.^[6]

Desktop Virtualization/Virtual Desktop Infrastructure (VDI). The application is hosted in a VM or blade PC that also includes the operating system (OS). These solutions include a management infrastructure for automating the creation of virtual desktops, and providing for access control to target virtual desktop. VDI solutions can usually fill the gaps where application streaming falls short.

Benefits of application virtualization

Allows applications to run in environments that do not suit the native application (e.g. Wine allows Microsoft Windows applications to run on Linux).
May protect the operating system and other applications from poorly written or buggy code and in some cases provide memory protection and IDE style debugging features ^[7].
Uses fewer resources than a separate virtual machine.
Run applications that are not written correctly, for example applications that try to store user data in a read-only system-owned location.
Run incompatible applications side-by-side, at the same time^[6] and with minimal regression testing against one another.^[8]
Reduce system integration and administration costs by maintaining a common software baseline across multiple computers in an organization.
Implement the security principle of least privilege by removing the requirement for end-users to have Administrator privileges in order to run poorly written applications.
Simplified operating system migrations.^[6]
Accelerated application deployment, through on-demand application streaming.^[6]
Improved security, by isolating applications from the operating system.^[6]
Enterprises can easily track license usage. Application usage history can then be used to save on license costs.
Fast application provisioning to the desktop based upon user's roaming profile.
Allows applications to be copied to portable media and then imported to client computers without need of installing them.^[9]

Limitations of application virtualization

Not all software can be virtualized. Some examples include applications that require a device driver and 16-bit applications that need to run in shared memory space.^[10]
Some types of software such as anti-virus packages and applications that require heavy OS integration, such as Stardock's WindowBlinds or TGTSoft's StyleXP are difficult to virtualize.
Only file and registry-level compatibility issues between legacy applications and newer operating systems can be addressed by application virtualization. For example, applications that don't manage the heap correctly will not execute on Windows Vista as they still allocate memory in the same way, regardless of whether they are virtualized or not.^[11] For this reason, specialist application compatibility fixes (shims) may still be needed, even if the application is virtualized.^[12]

References

^ "Microsoft Application Virtualization Technical Overview". Microsoft. http://www.microsoft.com/systemcenter/appv/techoverview.mspx.
^ "WritePrivateProfileString Function". Microsoft. http://msdn.microsoft.com/en-us/library/ms725501(VS.85).aspx. Retrieved 2008-06-18.
^ Mark Russinovich (June 2007). "Inside Windows Vista User Account Control". Microsoft. http://www.microsoft.com/technet/technetmag/issues/2007/06/UAC/default.aspx.
^ Amir Husain. "How to build an Application Virtualization Framework". VDIworks. http://vdiworks.com/wp/?p=15. Retrieved 2008-07-01.
^ Coby Gurr (2008-01-28). "Facilitating Microsoft Windows Vista Migration Through Application Virtualization" (PDF). Dell. http://www.dell.com/downloads/global/power/ps1q08-20080154-LANDesk.pdf. Retrieved 2008-06-19.
^ ^a ^b ^c ^d ^e "Desktop Virtualization Comes of Age" (PDF). Credit Suisse. 2007-11-26. http://www.dabcc.com/documents/DesktopVirtualization_11_26_07.pdf. Retrieved 2008-03-03.
^ http://en.wikipedia.org/wiki/IBM_OLIVER_%28CICS_interactive_test/debug%29
^ "Overview Series: Windows Vista Application Compatibility". Microsoft. http://technet2.microsoft.com/WindowsVista/en/library/006bca87-10df-4174-94b9-ed568a3faf991033.mspx?mfr=true. Retrieved 2008-06-19.
^ Domagoj Pernar (October 2009). "Application Virtualization Download repository, and how to make applications portable". V-irtualization.com. http://v-irtualization.com/2009/10/31/virtual-applications-app-v-download-repository/. Retrieved 2009-10-30.
^ Peter Varhol (September 2007). "Application Virtualization Hits Its Stride". Redmondmag.com. http://redmondmag.com/features/article.asp?editorialsid=1776. Retrieved 2008-06-19.
^ Adrian Marinescu (2006-07-14). "Windows Vista Heap Management Enhancements" (PDF). Microsoft. http://www.blackhat.com/presentations/bh-usa-06/BH-US-06-Marinescu.pdf. Retrieved 2008-06-19.
^ Chris Jackson (2008-05-01). "Can You Shim Applications Virtualized in SoftGrid?". Microsoft. http://blogs.msdn.com/cjacks/archive/2008/04/30/can-you-shim-applications-virtualized-in-softgrid.aspx. Retrieved 2008-06-24.