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Vol. 3A 4-17

PAGING

Table 4-10.  Format of a PAE Page-Directory Entry that References a Page Table

Bit 

Position(s)

Contents

0 (P)

Present; must be 1 to reference a page table

1 (R/W)

Read/write; if 0, writes may not be allowed to the 2-MByte region controlled by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 2-MByte region controlled by this entry (see 

Section 4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the page table referenced by this 

entry (see Section 4.9)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the page table referenced by this 

entry (see Section 4.9)

5 (A)

Accessed; indicates whether this entry has been used for linear-address translation (see Section 4.8)

6

Ignored

7 (PS)

Page size; must be 0 (otherwise, this entry maps a 2-MByte page; see Table 4-9)

11:8

Ignored

(M–1):12

Physical address of 4-KByte aligned page table referenced by this entry

62:M

Reserved (must be 0)

63 (XD)

If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 2-MByte region controlled 

by this entry; see Section 4.6); otherwise, reserved (must be 0)

Table 4-11.  Format of a PAE Page-Table Entry that Maps a 4-KByte Page

Bit 

Position(s)

Contents

0 (P)

Present; must be 1 to map a 4-KByte page

1 (R/W)

Read/write; if 0, writes may not be allowed to the 4-KByte page referenced by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 4-KByte page referenced by this entry (see Section 

4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the 4-KByte page referenced by 

this entry (see Section 4.9)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the 4-KByte page referenced by this 

entry (see Section 4.9)

5 (A)

Accessed; indicates whether software has accessed the 4-KByte page referenced by this entry (see Section 4.8)

6 (D)

Dirty; indicates whether software has written to the 4-KByte page referenced by this entry (see Section 4.8)

7 (PAT)

If the PAT is supported, indirectly determines the memory type used to access the 4-KByte page referenced by this 

entry (see Section 4.9.2); otherwise, reserved (must be 0)

1

8 (G)

Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise