Altiris SVS is based on file system redirection technology, a concept that is not unique to Altiris. File system redirection is also used by Microsoft in Vista to provide backward compatibility with legacy apps that do not run in standard user mode (see this), which is a very specific and relatively simple use of the technology.
Altiris has a much broader vision for how redirection can be used. Altiris uses file system redirection to abstract any software-any application, data or patch-from the base operating environment, into prioritized layers that are portable between machines. We also abstract out the user-specific elements of all of these layers, together with user-specific OS settings, which we can then make portable.
The layering concept is unique to Altiris and is the basis for several patent applications. This enables SVS to provide faster, non-intrusive provisioning and deprovisioning, state maintenance and conflict elimination, all leveraging the native Windows security controls. Microsoft specifically states that their legacy app compatibility feature can create conflicts and that it bypasses user-based security. The portability concept also goes well beyond Microsoft’s use of redirection.
It is important not to confuse one special-function use of file system redirection with Altiris’ complete software virtualization strategy.