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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 core on which they are executed. A fully virtualized application is not installed in the traditional sense, although it is still executed as if it is. 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. Thus, the term "Application virtualization" is somewhat misleading, as it is the components of an Operating System that typically surround an application (e.g. registry, file system etc.) that are virtualized, not the application itself. A guest Operating System encapsulated within a virtual machine is not termed "Operting System virtualization" but hardware virtualization, as it is the physical hardware that is virtual.

Limited application virtualization is used in modern operating systems such as Microsoft Windows and Linux. For example, IniFileMappings were introduced with Windows NT to virtualize (into the Registry) the legacy INI files of applications originally written for Windows 3.1. Similarly, Windows Vista implements limited file and Registry virtualization so that legacy applications that try to save user data in a system location that was writeable in older versions of Windows, but is now only writeable by highly privileged system software, can work on the new Windows system without the obligation of the program having higher-level security privileges (which would carry security risks).

Full application virtualization requires a virtualization layer. 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. 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 Ceedo, InstallFree, Citrix XenApp, Novell ZENworks Application Virtualization, Endeavors Technologies Application Jukebox, Microsoft Application Virtualization, Software Virtualization Solution, and VMware ThinApp.

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.
  • 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 and with minimal regression testing against one another.
  • Maintain a standard configuration in the underlying operating system across multiple computers in an organization, regardless of the applications being used, thereby keeping costs down.
  • 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.
  • Accelerated application deployment, through on-demand application streaming.
  • Improved security, by isolating applications from the operating system.
  • 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.

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.
  • Some types of software such as anti-virus packages and application that require heavy OS integration, such as Windowblinds or 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. For this reason, specialist application compatibility fixes ("SHIMs") may still be needed, even if the application is virtualized.

 

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