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Let's review what happens when the CPU accesses a non-resident virtual page, i.e., a page with its resident bit set to 0. In the example shown here, the CPU is trying to access virtual page 5. In this case, the MMU signals a page fault exception, causing the CPU to suspend execution of the program and switch to the page fault handler, which is code that deals with the page fault. The handler starts by either finding an unused physical page or, if necessary, creating an unused page by selecting an in-use page and making it available. In our example, the handler has chosen virtual page 1 for reuse. If the selected page is dirty, i.e., its D bit is 1 indicating that its contents have changed since being read from secondary storage, write it back to secondary storage. Finally, mark the selected virtual page as no longer resident. In the "after" figure, we see that the R bit for virtual page 1 has been set to 0. Now physical page 4 is available for re-use. Are th...