Memory fragmentation and paging mechanism

1. Physical Address and logical address

logical address, linear address, physical address

8086CPU:

Physical Address: Segment Address *16+ offset (20-bit bus address)

Logical Address: Page *16+ offset (16-bit register address)

after 8086CPU, the bus addressing and CPU bit convergence, the operating system structure is backward-compatible, linear address base 0:

Virtual address ( linear address ): Virtual address space per process 32-bit operating system 4G, 1G kernel page, 3G user page (32-bit CPU register address)

personal opinion: Linear address, segment descriptor limits physical memory space address, makes memory fully utilized

Physical Memory Partitioning: Frame logical memory Partitioning: page

address bus : Intel early CPU20 bit ( memory 1M), 286 address bus 24 bits ( memory 64M), 386 address bus 32 bits ( memory 4G)

Bus: Address bus, data bus, control bus

2. Software and hardware implementation of page table

Page Table: section storage and page number table, the following page table

implementation: Hardware using TLB (translation look-aside buffer translation fallback buffer) + memory storage

3. Segment Table Hardware structure

Segment Table: Base address + boundary register (limit offset size)

4. Logical address StructureLogical Address = Segment Selector + intra-segment offset

Segment Selector , index number corresponds to segment descriptor

the segment descriptor is stored in:                   

GDT (Global Descriptor table, descriptor table), GDTR register Save segment Descriptor

LDT (Local Descriptor table, native description table), LDTR register save segment descriptor, such as a single process

5. Logical address to linear address    

Segment selector: ti=0 using the LDT with Gdt,ti=1

6. Page table data structure (for example: segment Description Fu selector)

A. Hierarchy page (hierarchical Paging)

B.Hashed page Tables Hash page table

This article refers to the following information, the image reference from this, this article only to do summary:

Http://www.cnblogs.com/felixfang/p/3420462.html

http://blog.csdn.net/drshenlei/article/details/4261909

Http://wenku.baidu.com/link?url=6vkfCHh2LeGvc6PfxmmrqKXkv4oM3S6PujD_ Mdbdiybjvi5by5yycrydvaqo7t13wecaebj9cube6aqrc6ct_rjt6zfkkxjb8armqggbuz_

Http://blog.chinaunix.net/uid-22683402-id-1771372.html

Http://bbs.chinaunix.net/thread-2083672-1-1.html

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Memory fragmentation and paging mechanism