n When does a modified page should be written out to disk? n Demand cleaning u a page is written out only when it’s frame has been selected for replacement F but a process that suffer a page fault may have to wait for 2 page transfers n Precleaning u modified pages are written before their frame are needed so that they can be written out in batches F but makes little sense to write out so many pages if the majority of them will be modified again before they are replaced