Memory segmentation in the 80386 processor allows programs to access separate segments of memory. Segments are defined by descriptors that specify attributes like the base address, length, type and privilege level. Descriptors are stored in tables like the Global Descriptor Table which the processor uses to enforce memory access privileges and boundaries for each segment.

1. Memory Segmentation

7. Segment Descriptors field Base Address of segment (0-FFFFFFFF) Length of segment (0-FFFFFFFF) Segment Type Privilege Level Miscellaneous

8. Segment Descriptor format

18. GDT GDT 0 GDT 1 GDT 2 GDTR Offset Index 2 1 0 TI RPL

19. SEGMENTATION Addressing GDT Prog GDT Main Memory Index 2 1 0 TI RPL GD 0 GD 1 GD 2 GDTR Offset

20. Addressing GDT GD 0 GD 1 GD 2 Main Memory Base Address Seg Limit Attrib Index 3 2 1 0 TI RPL GDTR Offset

21. GD 0 GD 1 GD 2 GDTR Index 2 1 0 TI RPL GDT Base Address Seg Limit Attrib + Offset

23. Descriptor LDT Descriptor Descriptor Descriptor Data Descriptor Descriptor GDT LDT GDTR LDTR 1 DS ESI