Demand paging is a fundamental part of today's computer systems. Understanding demand paging performance is critical if we are to analyze and predict the performance for large-scale applications. This work presents experiments that illuminate the meaning of paging performance metrics available under Windows NT. We find that under some memory access conditions the Windows NT Cache manager will induce more paging activity than is explicitly requested by an application while at the same time, paging activity is not attributed to the application at all. 1 Introduction Nearly all modern operating systems use demand paging in order to provide today's applications with the large address spaces they require. Demand paging creates the illusion of an address space that is larger than physical memory by keeping currently unused pages on disk. This address space increase is not with out cost as while disk speeds have increased tremendously in recent years, they are still at least three orders of ..