69e17a6a_otected_Mode_Memory_Management__Designated_Role
[Field] Type [Designated Role] 
Segment Type (4-bits) When the descriptor entry describes a code segment, this field determines the type of the segment: execute-only or execute-read, conforming or non-conforming. When the descriptor entry describes a data segment, this field determines the type of the segment: read-only or read-write, expand-down or expand-up. Accessesing an expand-up segment with an offset which exceeds the segment limit value, causes an exception. The limit field in expand-down data segments is treated differently by the processor. Offsets which cause an exception to occur in expand-up segments are valid in expand-down segments. An access into an expand-down segment must be done with an offset larger than the segment limit or else an exception is generated. Decreasing the segment limit value in an expand-down segment causes memory to be allocated at the bottom of the segment. This is very useful for stacks since they tend to grow toward lower memory addresses.
Protected-Mode Memory Management
Designated Role