The fetch policy where a page is brought into main memory only if a reference is made to a location on that page is called .

The fetch policy you are referring to is known as "demand paging."

In demand paging, the operating system loads a page into main memory only when a process attempts to access a memory location on that page. This approach contrasts with other policies, such as "prepaging," where pages are loaded into memory ahead of time, anticipating that they will be needed. The advantage of demand paging lies in its efficiency, as it limits memory usage by only loading necessary pages, which is particularly beneficial in systems with limited memory resources. It also helps reduce load times since pages that are never referenced are never brought into memory, allowing for better overall system performance. Demand paging is widely used in modern operating systems to manage memory more effectively, balancing between responsiveness and resource utilization.