\WINDOWS\system32\dllcache
it is hidden system folder, you won't see it until "Hide protected ..system folders/files ..blah blah blah" will be disabled.
That folder keeps copy of every system file in \system32 folder in case one of those files will be deleted or else, system copies original from \dllcache to "save the system" from "corruption", kapish'?
..this is very useful and helpful place for information...