Fixing the MBR without the recovery console?

  • Thread starter Thread starter Massimo
  • Start date Start date
Timothy said:
"Bill in Co." asked:


Not quite - adding or replacing or subtracting a hard drive from
the system does not affect the MBR of any of the hard drives. The
MBR pertains to just what is on its own hard drive.

*TimDaniels*
Click to expand...

Right - thanks for catching that. :-)
 
I'm not sure I understand that. If you make any change in partitions to
the hard drive, it HAS to be reflected in the MBR and the partition
tables,
doesn't it?
Click to expand...

Normally, yes.

But in this case Acer modified the MBR code to automatically mark the first
partition of the disk as a hidden recovery partition, so this happens
everytime that code gets executed (i.e. everytime the BIOS loads that MBR
when booting). This is done on the assumption that the first partition is
the Acer recovery one and the second one contains the actual operating
system, so, if this doesn't match your disk layout (because you
repartitioned it), the Acer MBR code ends up screwing up your partition
table.

Think of it as a good old MBR-residing virus...


Massimo
 
Massimo said:
Normally, yes.

But in this case Acer modified the MBR code to automatically mark the first
partition of the disk as a hidden recovery partition, so this happens
everytime that code gets executed (i.e. everytime the BIOS loads that MBR
when booting). This is done on the assumption that the first partition is
the Acer recovery one and the second one contains the actual operating
system, so, if this doesn't match your disk layout (because you
repartitioned it), the Acer MBR code ends up screwing up your partition
table.

Think of it as a good old MBR-residing virus...
Click to expand...

OK, now this is scaring me a bit. I've got a Dell, which uses something
similar (well, at least I know it uses two special partitions, and that the
second partition is where the WinXP op system is located). (I'm not sure
if it does this - what your Acer did, though).

I *do* know that just trying to use Boot It NG to examine it (even in
maintenance mode) screwed it up, and I had to restore the MBR from a backup,
and maybe that is related to what you just said - about it always being
rewritten at bootup.

Or maybe I'm still confused about this.
 
If one (finally) decides they don't want to keep those hidden Acer or Dell
partitions, can one "simply" delete those extra partitions, fix the MBR with
some utility program (on a floppy disk in my case), and change the boot.ini
file to reflect which is the new boot partition number? Is that what
you do that?
 
If one (finally) decides they don't want to keep those hidden Acer or Dell
partitions, can one "simply" delete those extra partitions, fix the MBR
with
some utility program (on a floppy disk in my case), and change the
boot.ini
file to reflect which is the new boot partition number? Is that what
you do that?
Click to expand...

Yes, that's exactly what I did.
If Acer didn't have modified the MBR, using Partition Magic from another
computer and modifying the BOOT.INI would have been enough; but since the
MBR was indeed modified, I needed to fix it, and this got quite difficult to
do because the recovery console wasn't able to access the disk controller
and the laptop didn't have a floppy drive to supply a proper driver.


Massimo
 
Check your documentation - usually an utility is provided to copy the
recovery partition to removeable media (CD/DVD) and another to delete the
recovery partition and modified MBR - keep in mind that you can delete the
partition and put up with the "HitF10 to restore...." message at boot.
 
Bill said:
OK, now this is scaring me a bit. I've got a Dell, which uses something
similar (well, at least I know it uses two special partitions, and that the
second partition is where the WinXP op system is located). (I'm not sure
if it does this - what your Acer did, though).

I *do* know that just trying to use Boot It NG to examine it (even in
maintenance mode) screwed it up, and I had to restore the MBR from a backup,
and maybe that is related to what you just said - about it always being
rewritten at bootup.

Or maybe I'm still confused about this.
Click to expand...

Booting the machine with a bootitng install media and then entering
maintenance mode to examine the layout should not change anything.
Installation will change the partition table, mbr code will certainly be
changed if you elect to permit unlimited primaries. Not sure about
limited primaries if the mbr is non std to begin with.
Worth getting their free mbrwork.exe file from www.terabyteunlimited.com
to save/restore mbr plus some other dangerous stuff.
Dave Cohen
 
Dave said:
Booting the machine with a bootitng install media and then entering
maintenance mode to examine the layout should not change anything.
Click to expand...

Should not. But it DOES. (And I've verified that several times, no
matter what options I've selected or deselected so far)
Installation will change the partition table, mbr code will certainly be
changed if you elect to permit unlimited primaries.
Click to expand...

Nope - I *never* select that option to permit unlimited primaries. I'm
always quite conservative in that regard. :-)

Bottom line - I can't use it with my new WinXP computer at this point,
because it *does* screw up something (in Maintenance Mode - no matter what
I've tried so far). But it works perfectly and does NOT mess up anything
with my older Win98SE computer.
Not sure about
limited primaries if the mbr is non std to begin with.
Worth getting their free mbrwork.exe file from www.terabyteunlimited.com
to save/restore mbr plus some other dangerous stuff.
Dave Cohen
Click to expand...

Well, I have HAD to use a MBRSAVER utility to get me out of this jam (each
time I've tried Boot It NG on this new computer). And I don't like that
one bit. As I said, it works perfectly on the old Win98SE computer - no
problems.
 
Bill said:
Should not. But it DOES. (And I've verified that several times, no
matter what options I've selected or deselected so far)


Nope - I *never* select that option to permit unlimited primaries. I'm
always quite conservative in that regard. :-)

Bottom line - I can't use it with my new WinXP computer at this point,
because it *does* screw up something (in Maintenance Mode - no matter what
I've tried so far). But it works perfectly and does NOT mess up
anything
with my older Win98SE computer.


Well, I have HAD to use a MBRSAVER utility to get me out of this jam (each
time I've tried Boot It NG on this new computer). And I don't like that
one bit. As I said, it works perfectly on the old Win98SE computer - no
problems.
Click to expand...

UPDATE: I found the problem (with help from the author). When using BING
in Maintenance Mode, just go with the default checkboxes and don't check the
Limit Primaries box, as it overwrites the MBR incorrectly (for the Dell with
its other partitions). Good news.
 
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