Norton Update cache

General question, not a worry. I have a Vista Home Premium OS with Vista Service pack one.

When I go to the Vista Security location, there is an Icon for Symantec. When I open that it gives me the Live Update Configuration. There is a tab marked Current cache size.

My question- When I download Norton updates, the cache grows. Does this mean that the update has been downloaded but NOT yet installed? Or does this cache hold a copy of the update? I think my settings have the Norton updates set to automatically look for updates every 4 hours, download and install. I know whenever I do a manual live update check and there are updates, they download and install. When I check the cache after that the cache has grown.  Just wondering why they are in cache if they have been installed already