Vista MBR vs. XP MBR

[jorgen]

rewriting the disk signature with the Windows 98 fdisk /mbr command will
cause a boot failure. In most cases Windows 2000/XP will hardly bat an
eye and boot as if nothing had happened when the signature is rewritten,
Vista on the other hand will not boot if the disk signature is changed.

Then you also change more than just the program code. And it fails
because bootmgr stores the signature in its database. Unlike in
ntldr/boot.ini where you use the physical location, bootmgr uses the
disk signature. Vista's boot manager itself still loads just fine, it
just halts when it cannot find the new signature in the database.

The hole point was that the MBR only has one job, and the job is the
same whether you run vista or xp

 

[John John]

The hole point was that the MBR only has one job, and the job is the
same whether you run vista or xp

I don't think anyone said any differently. My point was that replacing
the Vista MBR may prevent Vista from booting properly, and it will if
you replace it with the standard W98 MBR and it may if you replace it
with the Windows 2000/XP MBR. For earlier Windows versions it hardly
mattered but replacing the Vista MBR with a different version is not a
recommended practice.

John

 

[John John]

I think all three are fine operating systems and I wouldn't have any
problems recommending any of these operating systems. It all depends on
what the user's needs are and what he or she does with the computer.

John

 

[jorgen]

I don't think anyone said any differently. My point was that replacing
the Vista MBR may prevent Vista from booting properly, and it will if
you replace it with the standard W98 MBR and it may if you replace it
with the Windows 2000/XP MBR. For earlier Windows versions it hardly
mattered but replacing the Vista MBR with a different version is not a
recommended practice.

It won't break because you replace it with a W98 MBR, it breaks because
fdisk does more than it should. It you use another tool that doesn't
wipe the signature, it will work the same

 

[John John]

It won't break because you replace it with a W98 MBR, it breaks because
fdisk does more than it should. It you use another tool that doesn't
wipe the signature, it will work the same

....unless or until the user decides he wants to enable BitLocker.

John

 

[jorgen]

I don't think anyone said any differently.

Actually, the discussion started because Timothy Daniels said otherwise.
The source he referred to stated that the specific boot loader was
installed in the MBR and not the the partition boot sector

 

[jorgen]

...unless or until the user decides he wants to enable BitLocker.

Unless I've misunderstood the concept, it wont break there either. It
will only break/go into recovery mode if you change the mbr while
bitlocker is active.

 

[John John]

Unless I've misunderstood the concept, it wont break there either. It
will only break/go into recovery mode if you change the mbr while
bitlocker is active.

Yes, I think that is correct. It will break if you change the MBR
*after* BitLocker is enabled, the MBR hash is only crated and stored in
the TPM's Platform Configuration Register when BitLocker is enabled, so
when BitLocker is enabled it should/will just create the hash with the
existing MBR be it the Vista MBR or another one, I think.

John

 

[CZ]

OT:

John:

You appear to be a non-zealous person.
May I ask your opinion re: Linux vs Vista vs Mac OS X?

TIA

John wrote:
I think all three are fine operating systems and I wouldn't have any
problems recommending any of these operating systems. It all depends on
what the user's needs are and what he or she does with the computer.


My response:
John:

So, you are a non-zealous person. The world needs more users like you.

 

[Timothy Daniels]

Actually, the discussion started because Timothy Daniels said otherwise. The
source he referred to stated that the specific boot loader was installed in
the MBR and not the the partition boot sector

Not true. The discussion started in the thread "Blank entries in
Boot.ini file" in microsoft.public.windowsxp.general where I
commented that there were web tutorials on restoring Vista's MBR
if it had been overwritten by an installation of XP, and you argued
that MBRs were generic.

Again, no one has said that Vista's MBR function is any different
from that of previous Windows MBRs - that is, to simply call the
executable code in the active partition's Boot Sector. The essence
of the discussion is whether *contents* of the MBRs of Vista and
previous Windows are different so as to justify reloading the Vista
MBR if it had been replaced by XP's MBR, ...OR... whether the
MBRs could be used interchangeably. So far in this discussion,
the answer appears to be "sometimes" - which implies that the
MBR recovery should be done as a standard practice unless the
user knows exactly whether some special condition existed or not.

*TimDaniels*

 

[jorgen]

Not true. The discussion started in the thread "Blank entries in
Boot.ini file" in microsoft.public.windowsxp.general where I
commented that there were web tutorials on restoring Vista's MBR
if it had been overwritten by an installation of XP, and you argued
that MBRs were generic.

Again, no one has said that Vista's MBR function is any different
from that of previous Windows MBRs - that is, to simply call the
executable code in the active partition's Boot Sector. The essence
of the discussion is whether *contents* of the MBRs of Vista and
previous Windows are different so as to justify reloading the Vista
MBR if it had been replaced by XP's MBR, ...OR... whether the
MBRs could be used interchangeably. So far in this discussion,
the answer appears to be "sometimes" - which implies that the
MBR recovery should be done as a standard practice unless the
user knows exactly whether some special condition existed or not.

You quoted from your source the following:

"Because you can't use the Windows XP bootloader to boot Vista,
we have to reinstate Vista's bootloader to the MBR and configure
it to manage both operating systems."

"The Windows XP bootloader gets installed to the MBR
and Vista can no longer boot." [......]


So yes, someone said something else

 

[Jawade]

It's stored in the MBR at offsets 1B8h through 1BBh.



Yes, I tried it with one of the Vista Release Candidates and Vista
failed to boot after the change. Maybe the final Vista release handles
disk signature changes differently?

I did made a XP-MBR on Vista and it works ok. Note te disk signature
belongs to the boot-partition and the 3 bytes at 01B5-01B7 belongs
to the IPL. The disk signature can you find back in the register at
the boot-partition at DosDevices.

 

[jorgen]

Yes, I think that is correct. It will break if you change the MBR
*after* BitLocker is enabled, the MBR hash is only crated and stored in
the TPM's Platform Configuration Register when BitLocker is enabled, so
when BitLocker is enabled it should/will just create the hash with the
existing MBR be it the Vista MBR or another one, I think.

I've looked briefly on the vista mbr, and there is actually a
bitlocker-related interrupt call in there. So it might be worth checking
that out some more

 

[CZ]

Re: disk signature:

It's stored in the MBR at offsets 1B8h through 1BBh.

John:

I just used Disk Probe via XP Pro and regedit in Vista SP1 on my dual boot
computer to confirm the data value and its location in the MBR and in
Vista's registry.

I may run the fdisk /mbr via Win 98 SE floppy boot disk test again.
Based on my previous test, I would not expect the disk signature to change.
It might be useful to know if SP1 makes a difference.

My previous test (and post):
David:

I did some testing to see if Vista does change the MBR.
On a Vista/Win XP dual boot computer, I ran fdisk /mbr from a Win98 SE
bootable floppy.

Results:
1) Vista's dual boot menu displayed in normal manner
2) Vista op system had a short prompt re: installing some drivers (could not
find what they they were about)
3) Vista's EventMgr did not have any relevant error messages
4) Vista ran in normal manner

5) When I selected "Other op systems" from the Vista dual boot menu, I
received an error message re: "ntldr" was missing, and the usual boot.ini
type of menu did not display

6) What I learned: The BCD store had been changed (note the "device
unknown" lines below)

Windows Boot Manager
--------------------
identifier {bootmgr}
device unknown
description Windows Boot Manager
locale en-US
inherit {globalsettings}
default {current}
resumeobject {50c73d4d-e6b3-11da-bc73-d30cdb1ce216}
displayorder {ntldr}
{current}
toolsdisplayorder {memdiag}
timeout 30

Windows Legacy OS Loader
------------------------
identifier {ntldr}
device unknown
path \ntldr
description Earlier version of Windows

Windows Boot Loader
-------------------
identifier {current}
device partition=C:
path \Windows\system32\winload.exe
description Microsoft Windows
locale en-US
inherit {bootloadersettings}
osdevice partition=C:
systemroot \Windows
resumeobject {50c73d4d-e6b3-11da-bc73-d30cdb1ce216}
nx OptIn

7) What I did to correct the problem: ran the following two cmds via Vista
Safe Mode boot:
Bcdedit /set {bootmgr} device partition=D:
Bcdedit /set {ntldr} device partition=D:

8) Summary:
I now have a computer dual booting Vista and Win XP via a Win98 SE MBR

 

[CZ]

Re: disk signature

Jorgen:

I just ran bcdedit /enum and did not see the disk signatrue listed.

How does one verify that it is in the BCD store?

 

[CZ]

Re: disk signature

Jorgen:

This makes sense to me:
"The Master Boot Record, created when you create the first partition on the
hard disk"

Above is per http://www.ntfs.com/mbr.htm

IMO, that is when the disk signature is created and would not be normally
recreated unless you repartition.

 

[CZ]

Re: disk signature

Jorgen:

Per the following only the program code in the MBR (sector 0) is replaced by
fdisk /mbr, suggesting that the disk signature is not changed.

From: http://support.microsoft.com/kb/69013

What is the MBR?
At the end of the ROM BIOS bootstrap routine, the BIOS reads and executes
the first physical sector of the first floppy or hard disk on the system.
This first sector of the hard disk is called the master boot record (or
sometimes the partition table or master boot block). There is a small
program at the beginning of this sector of the hard disk. The partition
information, or partition table, is stored at the end of this sector. This
program uses the partition information to determine which partition is
bootable (usually the first primary DOS partition) and attempts to boot from
it.

This program is written to the disk by the fdisk /mbr command and is usually
called the master boot record. During typical operation, Fdisk writes this
program to the disk only if there is no master boot record.

 

[John John]

I did made a XP-MBR on Vista and it works ok. Note te disk signature
belongs to the boot-partition and the 3 bytes at 01B5-01B7 belongs
to the IPL. The disk signature can you find back in the register at
the boot-partition at DosDevices.

Yes, the Windows 2000/XP MBR boots Vista without problems, so does the
Windows 98 MBR, as long as you edit and restore the disk signature after
you install it.

What exactly do you mean by "the disk signature belongs to the
boot-partition"? The disk signature is used (combined) in the creation
of all partition signatures on the disk, if you have more than one
partition the disk signature was used in (is part of) all the partition
signatures. The three bytes at offsets 1B5-1B7 are used to display
error messages from the Master Boot Code.

John

 

[John John]

Re: disk signature:



John:

I just used Disk Probe via XP Pro and regedit in Vista SP1 on my dual
boot computer to confirm the data value and its location in the MBR and
in Vista's registry.

I may run the fdisk /mbr via Win 98 SE floppy boot disk test again.
Based on my previous test, I would not expect the disk signature to change.

It does, CZ, there is absolutely no doubt about that, fdisk /mbr
rewrites the disk signature, that is a long well known characteristic of
the command, sometimes that "feature" can be used to advantage to
correct certain drive letter problems on Windows 2000/XP.

Fdisk /mbr rewrites the first 446 bytes of the MBR. Fixmbr, The Windows
2000/XP Recovery Console equivalent only rewrites the first 440 bytes.
The disk signature is held at bytes 440 to 443, just above the rewrite
threshold of fixmbr and within the extra six bytes that fdisk /mbr rewrites.

It might be useful to know if SP1 makes a difference.

You mean with DiskProbe? No, I don't think so. Give this Disk Editor a
try: http://mh-nexus.de/hxd/ I think you will like it better than
DiskProbe.

John

 

[Timothy Daniels]

It does, CZ, there is absolutely no doubt about that, fdisk /mbr rewrites the
disk signature, that is a long well known characteristic of the command,
sometimes that "feature" can be used to advantage to correct certain drive
letter problems on Windows 2000/XP.

Fdisk /mbr rewrites the first 446 bytes of the MBR. Fixmbr, The Windows
2000/XP Recovery Console equivalent only rewrites the first 440 bytes. The
disk signature is held at bytes 440 to 443, just above the rewrite threshold
of fixmbr and within the extra six bytes that fdisk /mbr rewrites.


You mean with DiskProbe? No, I don't think so. Give this Disk Editor a try:
http://mh-nexus.de/hxd/ I think you will like it better than DiskProbe.

John

So what is the bottom line? Is the XP MBR interchangeable with
Vista's MBR?

*TimDaniels*