There is no mode bit to disable segmentation. The use of paging, however, is optional.
These two mechanisms (segmentation and paging) can be configured to support simple single-program (or single task) systems, multitasking systems, or multiple-processor systems that used shared memory.
what is segmentation?
segmentation provides a mechanism for dividing the processor’s addressable memory space(called the linear address space) into smaller protected address spaces called segments.
Usage
Segments can be used to hold the code, data, and stack for a program or to hold system data structures (such as a TSS or LDT). If more than one program (or task) is running on a processor, each program can be assigned its own set of segments. The processor then enforces the boundaries between these segments and ensures that one program does not interfere with the execution of another program by writing into the other program’s segments.
The segmentation mechanism also allows typing of segments so that the operations that may be performed on a particular type of segment can be restricted.
How to locate a byte in a particular segment ?
a logical address (also called a far pointer) must be provided.
A logical address consists of a segment selector and an offset. The segment selector is a unique identifier for a segment. Among other things it provides an offset into a descriptor table (such as the global descriptor table, GDT) to a data structure called a segment descriptor. Each segment has a segment descriptor, which specifies the size of the segment, the access rights and privilege level for the segment, the segment type, and the location of the first byte of the segment in the linear
address space (called the base address of the segment). The offset part of the logical address is added to the base address for the segment to locate a byte within the segment. The base address plus the offset thus forms a linear address in the processor’s linear address space.
If paging is not used, the linear address space of the processor is mapped directly into the physical address space of processor. The physical address space is defined as the range of addresses that the processor can generate on its address bus.
标签：Segmentation,space,--,segments,concepts,program,address,segment,processor From： https://www.cnblogs.com/xiangsplayground/p/16853699.html