
AMD-K5 Processor
63
21062E/0—June 1997
AMD K86 Family BIOS and Software Tools Developers Guide
Preliminary Information
Figure 13 and Table 19 show the fields in CR4. Figure 16 and
Table 20 show the fields in a page-directory entry.
4-Kbyte page translation differs from 4-Mbyte page translation
in the following ways:
I
4-Kbyte Paging (Figure 14)
—Bits 31–22 of the linear address
select an entry in a 4-Kbyte page directory in memory,
whose physical base address is stored in CR3. Bits 21–12 of
the linear address select an entry in a 4-Kbyte page table in
memory, whose physical base address is specified by bits
31–22 of the page-directory entry. Bits 11–0 of the linear
address select a byte in a 4-Kbyte page, whose physical base
address is specified by the page-table entry.
4-Mbyte Paging (Figure 15)
—Bits 31–22 of the linear address
select an entry in a 4-Mbyte page directory in memory,
whose physical base address is stored in CR3. Bits 21–0 of
the linear address select a byte in a 4-Mbyte page in
memory, whose physical base address is specified by bits
31–22 of the page-directory entry. Bits 21–12 of the
page-directory entry must be cleared to 0.
I
Figure 16. Page-Directory Entry (PDE)
8
7
6
5
4
3
2
1
0
31
P
C
D
U
/
S
W
/
R
G
9
10
11
12
A
V
L
P
S
A
P
W
T
P
Table Base Address
Symbol
AVL
G
PS
A
PCD
PWT
U/S
W/R
P
Description
Available to Software
Global
Page Size 0 = 4 Kbytes
Reserved = 0
Accessed
Page Cache Disable
Page Writethrough
User/Supervisor
Write/Read
Present (valid)
Bits
11–9
8
7
6
5
4
3
2
1
0