In computer operating systems, demand paging (as opposed to anticipatory paging) is a method of virtual memory management. In a system that uses demand paging, the operating system copies a disk page into physical memory only if an attempt is made to access it (i.e., if a page fault occurs). It follows that a process begins execution with none of its pages in physical memory, and many page faults will occur until most of a process's working set of pages is located in physical memory. This is an example of lazy loading techniques.
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“Just as the performance of the vilest and most wicked deeds requires spirit and talent, so even the greatest demand a certain insensitivity which under other circumstances we would call stupidity.”
—G.C. (Georg Christoph)