DOS硬盘结构与硬盘主引导扇区简介

参考：

1.DOS分区体系的主引导记录扇区－MBR

http://sjhfml.blog.51cto.com/656700/129090

2.DOS分区概述

http://sjhfml.blog.51cto.com/656700/129088

3.维基百科

 

注意：“DOS分区”并不是以操作系统的不同而划定的分区体系，而是指使用“主引导记录(MBR)”的分区体系。Microsoft DOS、Linux以及基于IA32平台的FreeBSD和OpenBSD等操作系统都使用DOS分区体系。DOS分区是最常见也是最复杂的分区体系。

一、硬盘分区结构

下面是一张linux下的硬盘分区图

这个视频截图形象地展示了DOS体系硬盘的结构

1.第1扇区：主引导扇区MBR（主引导记录+分区信息表DPT+2字节标志）（上面这个图把主引导记录当作MBR了哈，注意下）

2.各个系统分区（4个主分区，扩展分区只能有1个且算作主分区）

注意：各个系统主分区只能存放一种操作系统，扩展分区不能按照操作系统，各系统分区具有自己的引导记录、文件分配表区、文件目录区以及数据区。

再添加个扩展分区后：

我们主要关注硬盘的主引导扇区

    MBR由446个字节的引导代码、64个字节的主分区表及2个字节的签名值“55AA”组成。

（1）引导代码。MBR接管系统的控制权后，引导代码负责对其他代码信息进行检查（比如查看是否有“55AA”有效标记）并进一步引导系统。

（2）分区表。分区表负责描述磁盘内的分区情况。

（3）“55AA”有效标志。“55AA”标志做为有效标志以通知系统该MBR扇区是否有效，如果该标志丢失或损坏，磁盘将会显示为“未初始化”。

如下表所示：

Structure of a Master Boot Record

Address			Description		Size in bytes
Hex	Oct	Dec
0000	0000	0	Code Area		440 (max. 446)
01B8	0670	440	Optional Disk signature		4
01BC	0674	444	Usually Nulls; 0x0000		2
01BE	0676	446	Table of primary partitions (Four 16-byte entries, IBM Partition Table scheme)		64
01FE	0776	510	55h	MBR signature; 0xAA55[1]	2
01FF	0777	511	AAh
MBR, total size: 446 + 64 + 2 =					512

看不懂？再来个表，看懂就行：）

             MBR扇区数据结构

字节偏移(十六进制)	字节数	描述
00～1BD	446	引导代码
1BE～1CD	16	分区表项1
1CE～1DD	16	分区表项2
1DE～1ED	16	分区表项3
1EE～1FD	16	分区表项4
1FE～1FF	2	签名值(55AA)

硬盘分区表由4个16B的分区信息表组成，每个信息表的结构如下表所示：

 Partition Record Format:
 =======================

  Offset  Size    Description
  ------ ------  -------------------------------------------------------
   00h    Byte    Boot Indicator (80h = active partition)

   01h    Byte    Partition start head 
   02h    Byte    Partition start sector (bits 0-5)
   03h    Byte    Partition start track (bits 8,9 in bits 6,7 of sector)

=> 04h    Byte    operating system indicator  [ See TABLE below ! ] 
                 ==========================
   05h    Byte    Partition end head
   06h    Byte    Partition end sector (bits 0-5)
   07h    Byte    Partition end track (bits 8,9 in bits 6,7 of sector)

   08h    DWORD   sectors preceding partition
   0Ch    DWORD   length of partition in sectors

分区表中的偏移量04h处的分区类型有如下：

 Values for Operating System indicator:
 =====================================

 00h    empty partition-table entry
 01h    DOS 12-bit FAT
 02h    XENIX root file system
 03h    XENIX /usr file system (obsolete)
 04h    DOS 16-bit FAT (up to 32M)
 05h    DOS 3.3+ extended partition
 06h    DOS 3.31+ Large File System (16-bit FAT, over 32M)
 =====================================================================
 07h    QNX
 07h    OS/2 HPFS
 07h    Windows NT NTFS
 07h    Advanced Unix
 07h    see partition boot record; could be any of the above or others

 Note:  For partition-type 07h, you need to inspect the partition's
        Boot Record for the actual file system type.
 =====================================================================
 08h    OS/2 (v1.0-1.3 only)
 08h    AIX bootable partition, SplitDrive
 08h    Commodore DOS
 08h    DELL partition spanning multiple drives
 -----------------------------------------------
 09h    AIX data partition
 09h    Coherent filesystem
 ------------------------------- 
 0Ah    OS/2 Boot Manager
 0Ah    OPUS
 0Ah    Coherent swap partition
 -------------------------------
 0Bh    Windows95 with 32-bit FAT
 0Ch    Windows95 with 32-bit FAT (using LBA-mode INT 13 extensions)
 0Dh
 0Eh  logical-block-addressable VFAT (same as 06h but using LBA-mode INT 13)
 0Fh  logical-block-addressable VFAT (same as 05h but using LBA-mode INT 13)
 10h    OPUS
 11h    OS/2 Boot Manager hidden 12-bit FAT partition
 12h    Compaq Diagnostics partition
 13h
 -------------------------------
 14h  (resulted from using Novell DOS 7.0 FDISK to delete Linux Native part)
 14h    OS/2 Boot Manager hidden sub-32M 16-bit FAT partition
 -------------------------------
 15h 
 16h    OS/2 Boot Manager hidden over-32M 16-bit FAT partition
 -------------------------------
 17h    OS/2 Boot Manager hidden HPFS partition
 17h    hidden NTFS partition
 -------------------------------
 18h    AST special Windows swap file ("Zero-Volt Suspend" partition)
 19h    Willowtech Photon coS
 1Ah
 1Bh    hidden Windows95 FAT32 partition
 1Ch    hidden Windows95 FAT32 partition (using LBA-mode INT 13 extensions)
 1Dh
 1Eh    hidden LBA VFAT partition
 1Fh
 20h    Willowsoft Overture File System (OFS1)
 ------------------------------------
 21h    officially listed as reserved
 21h    FSo2
 22h
 23h    officially listed as reserved
 24h    NEC MS-DOS 3.x
 25h
 26h    officially listed as reserved
 27h
 31h    officially listed as reserved
 32h
 33h    officially listed as reserved
 34h    officially listed as reserved
 35h
 36h    officially listed as reserved
 ------------------------------------
 37h
 38h    Theos
 39-3Bh
 3Ch    PowerQuest PartitionMagic recovery partition
 3D-3Fh
 40h    VENIX 80286
 41h    Personal RISC Boot
 41h    PowerPC boot partition
 42h    SFS (Secure File System) by Peter Gutmann
 43h
 44h
 45h    EUMEL/Elan
 46h    EUMEL/Elan
 47h    EUMEL/Elan
 48h    EUMEL/Elan
 49-4Eh
 4Fh    Oberon boot/data partition
 50h    OnTrack Disk Manager, read-only partition
 51h    OnTrack Disk Manager, read/write partition
 51h    NOVELL
 52h    CP/M
 52h    Microport System V/386
 53h    OnTrack Disk Manager, write-only partition???
 54h    OnTrack Disk Manager (DDO)
 55h    EZ-Drive (see also INT 13/AH=FFh"EZ-Drive")
 56h    GoldenBow VFeature
 57-5Bh
 5Ch    Priam EDISK
 5D-60h
 61h    SpeedStor
 62h
 ------------------------------------
 63h    Unix SysV/386, 386/ix
 63h    Mach, MtXinu BSD 4.3 on Mach
 63h    GNU HURD
 ------------------------------------
 64h    Novell NetWare 286
 64h    SpeedStore
 ------------------------------------
 65h    Novell NetWare (3.11)
 66h
 67h    Novell
 68h    Novell
 69h    Novell
 6A-6Fh
 70h    DiskSecure Multi-Boot
 ------------------------------------
 71h    officially listed as reserved
 72h
 73h    officially listed as reserved
 74h    officially listed as reserved
 ------------------------------------
 75h    PC/IX
 76h    officially listed as reserved
 ------------------------------------
 77-7Dh
 7Eh    F.I.X.
 7Fh
 80h    Minix v1.1 - 1.4a
 ------------------------------------
 81h    Minix v1.4b+
 81h    Linux
 81h    Mitac Advanced Disk Manager
 ------------------------------------
 82h    Linux Swap partition
 82h    Prime
 82h    Solaris (Unix)
 ------------------------------------
 83h    Linux native file system (ext2fs/xiafs)
 84h    OS/2-renumbered type 04h partition (related to hiding DOS C: drive)
 85h    Linux EXT
 86h    FAT16 volume/stripe set (Windows NT)
 ---------------------------------------------
 87h    HPFS Fault-Tolerant mirrored partition
 87h    NTFS volume/stripe set
 ---------------------------------------------
 88-92h
 93h    Amoeba file system
 94h    Amoeba bad block table
 95-98h
 99h    Mylex EISA SCSI
 9A-9Fh
 A0h    Phoenix NoteBIOS Power Management "Save-to-Disk" partition
 ------------------------------------
 A1h    officially listed as reserved
 A2h
 A3h    officially listed as reserved
 A4h    officially listed as reserved
 A5h    FreeBSD, BSD/386
 A6h    OpenBSD
 A7-A8h
 A9h    NetBSD ()
 AA-B0h
 B1h    officially listed as reserved
 B2h
 B3h    officially listed as reserved
 B4h    officially listed as reserved
 B5h
 B6h    officially listed as reserved
 ------------------------------------
 B7h    BSDI file system (secondarily swap)
 B8h    BSDI swap partition (secondarily file system)
 B9-BDh
 BEh    Solaris boot partition
 BFh
 C0h    DR-DOS/Novell DOS secured partition
 C0h    CTOS
 C1h    DR DOS 6.0 LOGIN.EXE-secured 12-bit FAT partition
 C2-C3h
 C4h    DR DOS 6.0 LOGIN.EXE-secured 16-bit FAT partition
 C5h
 C6h    DR DOS 6.0 LOGIN.EXE-secured Huge partition
 C6h    corrupted FAT16 volume/stripe set (Windows NT)
 -----------------------------------------------------
 C7h    Syrinx Boot
 C7h    corrupted NTFS volume/stripe set
 ----------------------------------------
 C8-CAh
 CBh    Reserved for DR-DOS secured FAT32
 CCh    Reserved for DR-DOS secured FAT32 (LBA)
 CDh
 CEh    Reserved for DR-DOS secured FAT16 (LBA)
 CFh
 D0h    Multiuser DOS secured FAT12
 D1h    Old Multiuser DOS secured FAT12
 D2-D3h
 D4h    Old Multiuser DOS secured FAT16 (<= 32M)
 D5h    Old Multiuser DOS secured extended partition
 D6h    Old Multiuser DOS secured FAT16 (> 32M)
 D7h
 D8h    CP/M-86
 D9-DAh
 DBh    CP/M, Concurrent CP/M, Concurrent DOS
 DBh    CTOS (Convergent Technologies OS)
 --------------------------------------------
 DC-E0h
 E1h    SpeedStor 12-bit FAT extended partition
 E2h    DOS read-only (Florian Painke's XFDISK 1.0.4)
 E3h    DOS read-only
 E3h    Storage Dimensions
 E4h    SpeedStor 16-bit FAT extended partition
 E5h    officially listed as reserved
 E6h    officially listed as reserved
 E7-EAh
 EBh    BeOS BFS (BFS1)
 EC-F0h
 F1h    Storage Dimensions
 F2h    DOS 3.3+ secondary partition
 F3h    officially listed as reserved
 F4h    SpeedStor
 F4h    Storage Dimensions
 F5h    Prologue
 F6h    officially listed as reserved
 F7-FDh
 FEh    LANstep
 FEh    IBM PS/2 IML (Initial Microcode Load) partition
 FFh    Xenix bad block table
 ----------------------------------------------------太多了，注意我们通常遇到的如82h,83h，还有NTFS分区07h

再来个形象的（没有分区）：

二、硬盘启动过程

1.机器加电；

2.BIOS加电自检。和软盘启动一样的

3.将硬盘0柱面0磁头1扇区的512B读入内存0000：7C00处；

4.检查0000：7DFE处是否等于0xAA55，若不等转去尝试其他启动介质，否则

5.跳转到0000：7C00执行MBR里的程序。

6.MBR首先复制自己到0000：0600处，然后继续执行。

7.引导程序在主分区表里搜索标志为活动的分区（有OS），如果没有或有不止一个，停止（？？？不止一个就停止？？）。

8.将活动分区的第一个扇区读入内存0000：7C00处。

9.检查0000：7DFE是否等于0xAA55，若不等，显示“Missing OS”然后停止，或尝试软盘启动

10.跳转到0000：7C00处继续执行特定系统的启动程序。

11.启动系统。

6-10由MBR中的引导程序完成。

复杂的多系统引导程序如NT loader，GRub等的原理差不多哈