Modern Hard Drives have large internal write cache. The cache will speed up writes since the drive can free the bus right after data has been written in cache. The drive then starts to write the data from cache by itself. That can be dangerous since all unwritten data in cache is lost if power is turned off or the system is reset. Modern operating systems will flush the cache when user shuts down the system. DOS does not have that sort of protection so it is up to the user to make sure cache is flushed. WARNING!!! Write cache should be left disabled.