AMD-K6 AMD [Advanced Micro Devices], AMD-K6 Datasheet - Page 63

• Manufacturer Part Number: AMD-K6
• Description: AMD-K6 Processor
• Manufacturer: AMD [Advanced Micro Devices]

20695H/0—March 1998
Figure 39. Page Table Entry (PTE)
Descriptors and Gates
Chapter 3
31
Symbol
PCD
PWT
U/S
W/R
P
AVL
D
A
Available to Software
Reserved
Dirty
Accessed
Page Cache Disable
Page Writethrough
User/Supervisor
Write/Read
Present (valid)
Description
Physical Page Base Address
There are various types of structures and registers in the x86
architecture that define, protect, and isolate code segments,
data segments, task state segments, and gates. These structures
are called descriptors.
Figure 40 on page 46 shows the application segment descriptor
format. Table 7 contains information describing the memory
segment type to which the descriptor points. The application
segment descriptor is used to point to either a data or code
segment.
Figure 41 on page 47 shows the system segment descriptor
format. Table 8 contains information describing the type of
segment or gate to which the descriptor points. The system
segment descriptor is used to point to a task state segment, a
call gate, or a local descriptor table.
The AMD-K6 processor uses gates to transfer control between
executable segments with different privilege levels. Figure 42
on page 48 shows the format of the gate descriptor types. Table
8 contains information describing the type of segment or gate
to which the descriptor points.
Software Environment
Bits
11–9
8–7
6
5
4
3
2
1
0
12
11
10
A
V
L
9
8
AMD-K6
7
D
6
®
5
A
Processor Data Sheet
D
4
P
C
W
3
P
T
2
U
S
/
W
1
R
/
P
0
45