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File - $Boot (7)

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Overview

This is the system file that allows the system to boot. This metadata file points at the boot sector of the volume. It contains information about the size of the volume, clusters and the MFT. It is the only file that cannot be relocated.

Attributes

Type Description Name
0x10 $STANDARD_INFORMATION  
0x30 $FILE_NAME $Boot
0x50 $SECURITY_DESCRIPTOR  
0x80 $DATA [Unnamed]

Layout of the File

Unnamed Data Stream

Offset Size Description
0x0000 3 Jump to the boot loader routine
0x0003 8 System Id: "NTFS    "
0x000B 2 Bytes per sector
0x000D 1 Sectors per cluster
0x000E 7 Unused
0x0015 1 Media descriptor (a)
0x0016 2 Unused
0x0018 2 Sectors per track
0x001A 2 Number of heads
0x001C 8 Unused
0x0024 4 Always 80 00 80 00
0x0028 8 Number of sectors in the volume
0x0030 8 LCN of VCN 0 of the $MFT
0x0038 8 LCN of VCN 0 of the $MFTMirr
0x0040 4 Clusters per MFT Record (b)
0x0044 4 Clusters per Index Record
0x0048 8 Volume serial number
~ ~ ~
0x0200   Windows NT Loader

(a) A media descriptor of 0xF8 means a hard disk
(b) Occasionally this can be 0xF6, which means 1/4

Notes

Other Information

The first 40 bytes are the same as for FAT boot sectors, except that unused fields are zeroed.

Because this file begins with a boot sector, it must start at physical cluster 0 (this is the only cluster that NTFS can not move). This forces the data attribute of this file to be non-resident. Consequently, the copy of the boot sector (critical data) can be located anywhere on the volume.

For crash recovery purposes Windows NT 3.51 saves a copy of the boot sector and puts it in the logical middle of the volume. Windows NT and later put it at the end of the volume.


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