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Table 5-1 describes the boot sector of a volume formatted with NTFS. When you format an NTFS volume, the format program allocates the first 16 sectors for the boot sector and the bootstrap code.
Table 5-1 NTFS Boot Sector
Byte Offset
| Field Length
| Field Name
| 0x00 | 3 bytes | Jump Instruction | 0x03 | LONGLONG | OEM ID | 0x0B | 25 bytes | BPB | 0x24 | 48 bytes | Extended BPB | 0x54 | 426 bytes | Bootstrap Code | 0x01FE | WORD | End of Sector Marker | On NTFS volumes, the data fields that follow the BPB form an extended BPB. The data in these fields enables Ntldr (NT loader program) to find the master file table (MFT) during startup. On NTFS volumes, the MFT is not located in a predefined sector, as on [wiki]FAT[/wiki]16 and FAT32 volumes. For this reason, the MFT can be moved if there is a bad sector in its normal location. However, if the data is corrupted, the MFT cannot be located, and Windows NT/2000 assumes that the volume has not been formatted.
The following example illustrates the boot sector of an NTFS volume formatted while running Windows 2000. The printout is formatted in three sections:
- Bytes 0x00- 0x0A are the jump instruction and the OEM ID (shown in bold print).
- Bytes 0x0B-0x53 are the BPB and the extended BPB.
- The remaining code is the bootstrap code and the end of sector marker (shown in bold print).
The following table describes the fields in the BPB and the extended BPB on NTFS volumes. The fields starting at 0x0B, 0x0D, 0x15, 0x18, 0x1A, and 0x1C match those on FAT16 and FAT32 volumes. The sample values correspond to the data in this example.
Byte Offset | Field Length | Sample Value | Field Name | 0x0B
| WORD
| 0x0002
| Bytes Per Sector
| 0x0D
| BYTE
| 0x08
| Sectors Per Cluster
| 0x0E
| WORD
| 0x0000
| Reserved Sectors
| 0x10
| 3 BYTES
| 0x000000
| always 0
| 0x13
| WORD
| 0x0000
| not used by NTFS
| 0x15
| BYTE
| 0xF8
| Media Descriptor
| 0x16
| WORD
| 0x0000
| always 0
| 0x18
| WORD
| 0x3F00
| Sectors Per Track
| 0x1A
| WORD
| 0xFF00
| Number Of Heads
| 0x1C
| DWORD
| 0x3F000000
| Hidden Sectors
| 0x20
| DWORD
| 0x00000000
| not used by NTFS
| 0x24
| DWORD
| 0x80008000
| not used by NTFS
| 0x28
| LONGLONG
| 0x4AF57F0000000000
| Total Sectors
| 0x30
| LONGLONG
| 0x0400000000000000
| Logical Cluster Number for the file $MFT
| 0x38
| LONGLONG
| 0x54FF070000000000
| Logical Cluster Number for the file $MFTMirr
| 0x40
| DWORD
| 0xF6000000
| Clusters Per File Record Segment
| 0x44
| DWORD
| 0x01000000
| Clusters Per Index Block
| 0x48
| LONGLONG
| 0x14A51B74C91B741C
| Volume Serial Number
| 0x50
| DWORD
| 0x00000000
| Checksum
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Protecting the Boot SectorBecause a normally functioning system relies on the boot sector to access a volume, it is highly recommended that you run disk scanning tools such as Chkdsk regularly, as well as back up all of your data files to protect against data loss if you lose access to a volume.
[ 本帖最后由 甜橙 于 2007-11-3 16:13 编辑 ] |
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