21. If the page number is not in the TLB, the page table must be checked. 22. The page table translates virtual memory addresses of a process to the physical memory pages. 23. The inverted page table keeps a listing of mappings installed for all frames in physical memory. 24. The IPT combines a page table and a " frame table " into one data structure. 25. It also uses the topmost bit of the 64-bit page table entry as an NX bit. 26. The page table lookup may also fail if the page is not resident in physical memory. 27. In 1996, Liedtke completed a PhD on guarded page tables at the Technical University of Berlin. 28. An overhead of 1 KiB of memory is required for maintaining page directories and page tables . 29. It is done by keeping several page tables that cover a certain block of virtual memory. 30. Tree-based designs avoid this by placing the page table entries for adjacent pages in adjacent locations.
