A package of Windows DLL files for applications written in Visual C++, Microsoft's predominant development environment. Automatically installed in Windows computers and updated periodically, users may find any number of these packages in their Programs control panel. There is a reason these sets of system software are added to and accumulate in the computer instead of overlaying existing files and having only one current version. Microsoft has no way of knowing if an application is dependent on the unique behavior of a routine in one of the DLLs that might have been extensively modified in a subsequent version. See Visual C++, DLL and redistributable.