Intel IA-32 Manuale Utente

Vol. 3A 3-33

PROTECTED-MODE MEMORY MANAGEMENT

CR4 has no affect on the page size when PAE is enabled.) With the PS flag set, the linear address
is divided into three sections:

•

Page-directory-pointer-table entry—Bits 30 and 31 provide an offset to an entry in the
page-directory-pointer table. The selected entry provides the base physical address of a
page directory.

•

Page-directory entry—Bits 21 through 29 provide an offset to an entry in the page
directory. The selected entry provides the base physical address of a 2-MByte page.

•

Page offset—Bits 0 through 20 provides an offset to a physical address in the page.

3.8.4

Accessing the Full Extended Physical Address Space
With the Extended Page-Table Structure

The page-table structure described in the previous two sections allows up to 4 GBytes of
the 64 GByte extended physical address space to be addressed at one time. Additional 4-GByte
sections of physical memory can be addressed in either of two way:

•

Change the pointer in register CR3 to point to another page-directory-pointer table, which
in turn points to another set of page directories and page tables.

•

Change entries in the page-directory-pointer table to point to other page directories, which
in turn point to other sets of page tables.

Figure 3-19. Linear Address Translation With PAE Enabled (2-MByte Pages)