Application virtualization

Method to encapsulate computer programs

Application virtualization is a software technology that encapsulates computer programs 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 were. The application behaves at runtime like it is directly interfacing with the original operating system and all the resources managed by it, but can be isolated or sandboxed to varying degrees. In this context, the term "virtualization" refers to the artifact being encapsulated (application), which is quite different from its meaning in hardware virtualization, where it refers to the artifact being abstracted (physical hardware).

Application virtualization allows applications to run in environments that do not suit the native application. For example, Wine allows some Microsoft Windows applications to run on Linux. Application virtualization reduces system integration and administration costs by maintaining a common software baseline across multiple diverse computers in an organization. Lesser integration protects the operating system and other applications from poorly written or buggy code. In some cases, it provides memory protection, IDE style debugging features and may even run applications that are not written correctly, for example applications that try to store user data in a read only system owned location. (This feature assists in the implementation of the principle of least privilege by removing the requirement for end users to have administrative privileges in order to run poorly written applications.) It allows incompatible applications to run side by side, at the same time Isolating applications from the operating system has security benefits as well, as the exposure of the virtualized application does not automatically entail the exposure of the entire OS. Applications can be transferred to removable media or between computers without the need of installing them, becoming portable software. Application virtualization uses fewer resources than a separate virtual machine.

Not all computer programs can be virtualized. Some examples include applications that require a device driver (a form of integration with the OS) and 16 bit applications that need to run in shared memory space. Anti virus programs and applications that require heavy OS integration, such as WindowBlinds or StyleXP are difficult to virtualize. Moreover, in software licensing, application virtualization bears great licensing pitfalls mainly because both the application virtualization software and the virtualized applications must be correctly licensed. While application virtualization can address file and Registry level compatibility issues between legacy applications and newer operating systems, 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. For this reason, specialist application compatibility fixes (shims) may still be needed, even if the application is virtualized. Functional discrepancies within the multicompatibility model are an additional limitation, where utility driven access points are shared within a public network. These limitations are overcome by designating a system level share point driver.