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 , 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. Application virtualization differs from operating system virtualization in that in the latter case, the whole operating system is virtualized rather than only specific applications.

Description

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 read-only system location can still work on the platform without elevating users' access.

Full application virtualization requires a virtualization layer. This layer must be installed on a machine to intercept all file and Registry operations of virtualized applications and transparently redirect these operations into a virtualised location. The application performing the file operations never knows that it's not accessing the physical resource it believes it is. In this way, applications with many dependent files and settings can be made portable by redirecting all their input/output to a single physical file, and traditionally incompatible applications can be executed side-by-side. Microsoft Application Virtualization, Software Virtualization Solution, and VMware ThinApp are examples of this technology for the Windows platform.

A common misconception is that a runtime environment is application virtualization. However a runtime layer is required for an application to be able to execute, while a virtualization layer is not.

A similar, but different principle is Operating system virtualizations which encapsulate the entire operating system from the hardware, as opposed to only the applications from the operating system.

Technologies

Technology categories that fall under application virtualization include:

• Application Streaming. The application is delivered in a package, that may include a subset of OS files and configuration settings. Running the package requires the installation of a lightweight client application. Packages are usually delivered over a protocol such as HTTP or RTSP. Application virtualization is commonly paired with application streaming to deliver applications on demand.