The 64-bit addressing mode ("long mode") is a superset of Physical Address Extensions (PAE); because of this, page sizes may be 4 KiB (212 bytes) or 2 MiB (221 bytes). Long mode also supports page sizes of 1 GiB (1073741824 (230) bytes). Rather than the three-level page table system used by systems in PAE mode, systems running in long mode use four levels of page table: PAE's "Page-Directory Pointer Table" is extended from four entries to 512, and an additional "Page-Map Level 4 (PML4) Table" is added, containing 512 entries in 48-bit implementations. A full mapping hierarchy of 4 KiB pages for the whole 48-bit space would take a bit more than 512 GiB of memory (about 0.195% of the 256 TiB virtual space).