On Fri, 25 Aug 2000, OKUJI Yoshinori wrote:
> From: [EMAIL PROTECTED]
> Subject: Re: Serious problem with booting NT
> Date: Fri, 25 Aug 2000 05:39:16 +0400 (MSD)
>
> > In LiLo CHANGES file:
> > -- cut --
> > - now only 0x1b8 bytes of the boot sector are overwritten, which preserves
> > some magic numbers NT stores there
> > -- cut --
>
> Do you know what the magic number is exactly or where I can find the
> official information?
>
This is not particular magic number. It's sort of "serial number for MBR".
I can not find information in online version of MSDN but it's described in
offline version (see attachment). When this magic number is overwritten by
GRUB connection between disk and registry is lost and names of drives are
changing randomly.
<HTML><HEAD><TITLE>Master Boot Record</title>
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<H3 CLASS="h2">Master Boot Record</H3><P CLASS="t">The Master Boot Record, created
when you create the first partition on the hard disk, is probably the most important
data structure on the disk. It is the first sector on the disk. The location is always
track (cylinder) 0, head (side) 0, and sector 1.</P>
<P CLASS="t">The Master Boot Record contains the Partition Table for the disk and a
small amount of executable code. On x86-based computers, the executable code examines
the Partition Table, and identifies the system partition. The Master Boot Record then
finds the system partition's starting location on the disk, and loads an copy of its
Partition Boot Sector into memory. The Master Boot Record then transfers execution to
executable code in the Partition Boot Sector.</P>
<P CLASS="t"><B>Note</B></P>
<P>Although there is a Master Boot Record on every hard disk, the executable code in
the sector is used only if the disk is connected to an x86-based computer and the disk
contains the system partition. </P>
<P CLASS="t">Figure 3.5 shows a hex dump of the sector containing the Master Boot
Record. The figure shows the sector in two parts. The first part is the Master Boot
Record, which occupies the first 446 bytes of the sector. The disk signature (FD 4E F2
14) is at the end of the Master Boot Record code. The second part is the Partition
Table.</P>
<P CLASS="spacing"><BR></P>
Physical Sector: Cyl 0, Side 0, Sector 1
00000000: 00 33 C0 8E D0 BC 00 7C - 8B F4 50 07 50 1F FB FC .3.....|..P.P..
00000010: BF 00 06 B9 00 01 F2 A5 - EA 1D 06 00 00 BE BE 07 ................
00000020: B3 04 80 3C 80 74 0E 80 - 3C 00 75 1C 83 C6 10 FE ...<.t..<.u.....
00000030: CB 75 EF CD 18 8B 14 8B - 4C 02 8B EE 83 C6 10 FE .u......L.......
00000040: CB 74 1A 80 3C 00 74 F4 - BE 8B 06 AC 3C 00 74 0B .t..<.t.....<.t.
00000050: 56 BB 07 00 B4 0E CD 10 - 5E EB F0 EB FE BF 05 00 V.......^.......
00000060: BB 00 7C B8 01 02 57 CD - 13 5F 73 0C 33 C0 CD 13 ..|...W.._s.3...
00000070: 4F 75 ED BE A3 06 EB D3 - BE C2 06 BF FE 7D 81 3D Ou...........}.=
00000080: 55 AA 75 C7 8B F5 EA 00 - 7C 00 00 49 6E 76 61 6C U.u.....|..Inval
00000090: 69 64 20 70 61 72 74 69 - 74 69 6F 6E 20 74 61 62 id partition tab
000000A0: 6C 65 00 45 72 72 6F 72 - 20 6C 6F 61 64 69 6E 67 le.Error loading
000000B0: 20 6F 70 65 72 61 74 69 - 6E 67 20 73 79 73 74 65 operating syste
000000C0: 6D 00 4D 69 73 73 69 6E - 67 20 6F 70 65 72 61 74 m.Missing operat
000000D0: 69 6E 67 20 73 79 73 74 - 65 6D 00 00 80 45 14 15 ing system...E..
000000E0: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
000000F0: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
00000100: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
00000110: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
00000120: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
00000130: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
00000140: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
00000150: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
00000160: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
00000170: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
00000180: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
00000190: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
000001A0: 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
000001B0: 00 00 00 00 00 00 00 00 - FD 4E F2 14 00 00 .........N....
80 01 ..
000001C0: 01 00 06 0F 7F 96 3F 00 - 00 00 51 42 06 00 00 00 .....?...QB....
000001D0: 41 97 07 0F FF 2C 90 42 - 06 00 A0 3E 06 00 00 00 A....,.B...>....
000001E0: C1 2D 05 0F FF 92 30 81 - 0C 00 A0 91 01 00 00 00 .-....0.........
000001F0: C1 93 01 0F FF A6 D0 12 - 0E 00 C0 4E 00 00 55 AA ...........N..U.
<P CLASS="cap"><B>Figure 3.5. Hex Dump of the Master Boot Record for an x86-based
computer</B></P>
<P CLASS="t">The disk signature is a unique number at offset 0x1B8 that
Windows NT uses as an index to store and retrieve information about the disk in
the Registry subkey HKEY_LOCAL_MACHINE\SYSTEM\DISK. The first time that you open Disk
Administrator after formatting a hard disk, it displays a dialog box that informs the
user that no disk signature was found on the disk. You should select <B>Yes</B>, or
Windows NT will not be able to access the disk.</P>
<P CLASS="t">Many destructive viruses can damage the Master Boot Record and make it
impossible to start the computer from the hard disk. Because the code in the Master
Boot Record executes before any operating system is started, no operating system can
detect or recover from corruption of the Master Boot Record. You can use the DiskProbe
program on Windows NT Server Resource Kit CD to display the Master Boot Record,
and compare it to the Master Boot Record shown in Figure 3.5. There are also utilities
on the Resource Kit that enable you to save and restore the Master Boot Record. See
Chapter 6, "Troubleshooting Disk and Startup Problems," and Chapter 7, "Disk, File
System, and Backup Utilities," for more information.</P>
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