SWV manages each Virtual Software Package (VSP) as a distinct entity. When they are activated, VSPs are like layers over the base Windows operating system. The VSPs make the system appear to contain the aggregate contents of the base operating system plus the active VSPs.
When a VSP is imported onto a computer, the contents of the VSP (both files and registry settings) are placed in a folder in a special protected SWV area on the hard dive. The area is often referred to as the SWV redirection area.
When a VSP is imported on a client computer, the contents of the VSP are placed in the redirected folder, such as C:\fslrdr\1. When the VSP is activated on a client computer, the contents of the VSP are made available to the user. The files and settings appear to the user in the location they would be in if the application had been installed on the computer.
Example: You have a VSP for Mozilla Firefox. When the Firefox VSP is activated, all the contents of the VSP are "layered" over the base file system and registry. The layering is what makes it visible to the user. The user then sees its appropriate folders, files, registry settings, and shortcuts. When the contents are made visible, they are not displayed in the hidden area. Instead they are displayed in the locations that the user would see them had Firefox been installed on the computer. Example: Even though the Firefox application file may physically be located at
Workspace Virtualization accomplishes the visibility by using a filter that intercepts requests to the file system and registry. SWV redirects requests to the active VSPs. Workspace Virtualization uses the SWV File System Filter Driver to aggregate the real and the virtual file systems into a single view for the user.
This process is displayed in the following figure:
The file system display in the lower left represents the "base" environment - Windows operating system files, data, and applications that were installed conventionally.
The file system display in the lower right represents virtualized data that is stored in the isolated, hidden redirection area.
The file system display at the top represents what the system, applications, and users see.
The SWV filter driver presents an aggregate view of the real file system and the layered virtual file system and registry. Gold represents data from the real file system. Blue represents data from a layer in the virtual file system. When an application or Windows requests a file, the request goes through the filter driver. The filter driver determines whether the request should be passed through to the real file system or redirected to a layer in the virtual file system.
If the file is in the real file system the request proceeds normally. If the filter driver determined that the file is in a layer in the virtual file system, the request is redirected to the layer files. In both cases, the application performs a normal file open request. The application has no idea that the filter driver is even there or what it does.
With redirection, SWV can maintain discrete settings and file versions for different applications on a single system. By working with VSPs, a required version of a file is never overwritten. The fact that it is never overwritten is particularly important when you work with dynamic link libraries (DLL). Incompatible .DLL files are known to cause application instability. By using applications within VSP, you can ensure that applications use their own sets of .DLL files. When applications use their own sets of .DDL files, they do not interfere with the rest of the operating system or other applications running at the same time.
Redirection extends not only to files that relate to applications, but also to registry settings and data files.