i'm just guessing that Windows does this way.
the system writes and reads everything, it should know if a cached information has been invalidated or not.
and even if the OS itself wouldn't do this way, the HDD at a lower level should notice the same sector being requested again and again, and provide the data directly from its cache, not bothering the magnetic discs.
i remember this behavior on MSDOS when i used smartdrive 15 years ago.
opinions?