Code Download installs most new code in a permanent store in windows\occache(11). Some components (helper DLLs that need to be on the system PATH but currently are not) will also be installed in \windows and \windows\system. All downloaded code is registered using a new registry "Module Usage" section that keeps track of such code. Downloaded code is not removed automatically, but it is possible in the future to add UI to the Control Panel (or elsewhere) allowing a user to clean up this directory.
For future releases, it is also possible to convert this "permanent store" into a code cache that retains only popular downloaded code and deletes old unused code automatically. This migration plan justifies use of a permanent store for the first version. See Appendix for registry details on how downloaded code is listed in the registry and how a code cache could function in future releases.