Intel IA-32 manual

3-18 Vol. 3A
PROTECTED-MODE MEMORY MANAGEMENT
See also: Section 3.5.1, “Segment Descriptor Tables”, and Section 6.2.2, “TSS Descriptor”
(for more information on the system-segment descriptors); see Section 4.8.3, “Call Gates”,
Section 5.11, “IDT Descriptors”, and Section 6.2.5, “Task-Gate Descriptor” (for more infor-
mation on the gate descriptors).
3.5.1 Segment Descriptor Tables
A segment descriptor table is an array of segment descriptors (see Figure 3-10). A descriptor
table is variable in length and can contain up to 8192 (213) 8-byte descriptors. There are two
kinds of descriptor tables:
•The global descriptor table (GDT)
•The local descriptor tables (LDT)
Figure 3-10. Global and Local Descriptor Tables
Segment
Selector
Global
Descriptor
T
First Descriptor in
GDT is Not Used
TI = 0
I
56
40
48
32
24
16
8
0
TI = 1
56
40
48
32
24
16
8
0
Table (GDT)
Local
Descriptor
Table (LDT)
Base Address
Limit
GDTR Register LDTR Register
Base Address
Seg. Sel.
Limit