In Windows XP there were always backups form the Windows Updates in a hidden directory in the %SystemRoot% folder (usually C:\Windows). This hidden directory is named after the Knowledge Base article for the relevant hotfix, such as $NtUninstallKB867282$, and contains an uninstallation utility. Some of them where fairly large. Especially the service packs that where as large as 500Meg. There were a lot of utilities to remove these hidden folders without removing the hotfix. For example, http://www.dougknox.com/xp/utils/xp_hotfix_backup.htm
At this time I am just very curious because in Windows 7 I don't see the hidden folders. Are they no longer kept, or are they just in a different place? I get a little freaked out because of the many Windows Defender updates that I receive. As I continue to use Windows 7, I want to know if I can manage any wasted hard drive space.