AMD-K6 AMD [Advanced Micro Devices], AMD-K6 Datasheet - Page 42

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

AMD-K6
Segment Registers
Segment Usage
24
®
Processor Data Sheet
The six 16-bit segment registers are used as pointers to areas
(segments) of memory. Table 4 lists the segment registers and
their functions. Figure 8 shows the format for all six segment
registers.
Table 4.
Figure 8. Segment Register
The operating system determines the type of memory model
that is implemented. The segment register usage is determined
by the operating system’s memory model. In a Real mode
memory model the segment register points to the base address
in memory. In a Protected mode memory model the segment
register is called a selector and it selects a segment descriptor
in a descriptor table. This descriptor contains a pointer to the
base of the segment, the limit of the segment, and various
protection attributes. For more information on descriptor
formats, see “Descriptors and Gates” on page 45. Figure 9 on
page 25 shows segment usage for Real mode and Protected
mode memory models.
Segment
Register
15
CS
DS
GS
ES
FS
SS
Code segment, where instructions are located
Data segment, where data is located
Data segment, where data is located
Data segment, where data is located
Data segment, where data is located
Stack segment
Segment Registers
Preliminary Information
Software Environment
Segment Register Function
0
20695H/0—March 1998
Chapter 3