69e17a6a_otected_Mode_Memory_Management__Designated_Role
[Field] D/B [Designated Role] 
Segment Size Bit When the descriptor entry describes a code segment, this bit is used to specify the default length of operands and addresses. When the bit is set, the processor assumes a 32-bit segment. When the bit is clear, a 16-bit segment is assumed. When the descriptor entry describes a data segment, this bit is used to control the operation of the stack. When this bit is set, stack operations use the ESP register. When this bit is clear, stack operations use the SP register.
Protected-Mode Memory Management
Designated Role