FDISK /MBR question

Am I right in thinking that the above command will repair a hard drive's
master boot record WITHOUT deleting any of the data contained on the drive?
It's a single-partition hard drive on a standard Dell-shipped machine.

TIA

 

Howdy!

Depends on what's wrong with the boot partition.

RwP

 

Am I right in thinking that the above command will repair a hard drive's

It's a standard machine which came with XP preinstalled. No other OS's on
there. AVG is reporting some MBR errors, and I'll be going over to see it
this evening, so I wanted to check if this option was do'able as one of the
possible solutions.

 

If you`ve had linux on your machine. you`ve probably had a boot loader on
your MBR. fdisk /MBR wiil put your boot record back to the standard Windows
MBR.
bw..OJ

 

There is nothing wrong with the MBR - it's a common problem at present with
AVG - ignore the error!!!

--
Noel Paton (MS-MVP 2002-2006, Windows)

Nil Carborundum Illegitemi
http://www.crashfixpc.com/millsrpch.htm

http://tinyurl.com/6oztj

Please read http://dts-l.org/goodpost.htm on how to post messages to NG's

 

AVG does show changes on several items. This has been asked before on here.
Whether the AVG forums have any info on that, I don`t know.
It`s never bothered me tho`.
Good luck for tonight.
bw..OJ

 

|>Am I right in thinking that the above command will repair a hard drive's
|>master boot record WITHOUT deleting any of the data contained on the drive?
|>It's a single-partition hard drive on a standard Dell-shipped machine.

In most cases yes, it only rewrites the boot sector and not the
partition tables.

Use the correct version of format, if you use Win98 format.com on an
XP OS your not going to boot up (in XP).

 

Am I right in thinking that the above command will repair a hard

Thanks to you and Noel for the reassurance.

 

The command you mention will erase the first 460 bytes of the MBR (master
boot record, the first physical sector of the hard drive and *outside* any
partition) which is the boot program. It overwrites that area with a
standard boot program. If you had anything else in the MBR boot program
area, you will wipe it out. Examples of other programs that occupy the boot
program area are: GoBack, multiboot managers, disk overlay managers (to
compensate for an old BIOS that cannot support large hard drives), and
security software (often which encrypts/decrypts the bytes within the
partitions or disk). So whether you should overwrite the MBR boot program
depends entirely on what is already there.

Also, a virus can move the partition table so it is not in the standard
offset within the MBR. The standard MBR boot program only knows to look in
the standard offset to find the partition table. The infected boot program
knows where to find the relocated partition table but the standard boot
program won't know where to look. The result is that the standard boot
program cannot find the partition table, tries to use whatever bytes are in
the standard offset for the partition table entries, and you end up not
being to access your partitions anymore.

If you want to overwrite the MBR boot program, first use a bootable floppy
to use a MBR backup utility to save what it already there. Then stomp on
the MBR boot program area using FDISK /MBR (or FIXMBR for Win2000/XP). Then
you can restore the old MBR boot program in case you really need it.

There is no "repairing" of the MBR boot program when using FDISK /MBR (or
FIXMBR). You end up OVERWRITING all those bytes.

 

Trax blabbered in 24hoursupport.helpdesk:

BWAHAHAHAHAHAHAHAHAHAAAAAAA!!!

 

Howdy!

XP? Then FDISK/MBR will make it unbootable.

Try the XP fix, FIXMBR from the Recovery Console.

RwP

 

Sorry to disagree RwP. I`ve just dumped a linux install off my system.
And used fdisk /MBR to get rid of the lilo booter.
It worked perfectly (WinXP SP2)
bw..OJ

 

Howdy!

Dunno where you found an FDISK that looked for NTLOADER instead of
IO.SYS then.

IOW - either you're confused, you've got a version of FDISK that
I've never seen, or you're out and out lying there, me boyo.

But the Win98 FDISK/MBR puts a boot strap that looks for IO.SYS to
continue. Which *ahem* doesn't work with any of the NT OSes.

I've had to recover several times from folks that do that.

Which is why XP and 2K's recovery consoles HAVE the FIXMBR command -
does the same thing, but the bootstrap code looks for NTLOADER instead of
IO.SYS .

RwP

 

WinMe boot disk.
bw..OJ

 

very strange boot disk, then! - I thought I'd used all varieties of that !

Care to mail me a copy of the files on the disk? - or the diskmaker file?
(my email is valid)



--
Noel Paton (MS-MVP 2002-2006, Windows)

Nil Carborundum Illegitemi
http://www.crashfixpc.com/millsrpch.htm

http://tinyurl.com/6oztj

Please read http://dts-l.org/goodpost.htm on how to post messages to NG's

 

Howdy!

Whose standard FDISK also installs looking for IO.SYS not NTLOADER.

VERY strange boot disk.

Care to send Noel a copy of it as a disk image? I'm sure Microsoft
would LOVE to have a copy of that FDISK ...

RwP

 

Read my prior post. The MBR bootstrap program *never* gives a gnat's fart
about which OS is installed in the active-marked partition. The BIOS loads
into memory the 460-byte area of the first sector of the first physically
detected hard drive (i.e., the MBR bootstrap program area) and then passes
control to it. That bootstrap program merely reads the partition table to
see which one is marked active and then loads the *partition's* boot sector
(the first sector of THAT partition) into memory and passes control to it.
That is all! It hasn't a clue about NTLOADER, IO.SYS, and any other files
*in* the file system *in* that partition. The OS has to put into its system
partition's boot sector whatever loader program it wants to use.

I've used FDISK /MBR in many cases where the OS was Windows NT4, Windows
2000, or Windows XP. Works just great providing there isn't a real need for
whatever already is occupying the MBR bootstrap program area (again, see my
prior post). Unless you have used some software, boot manager, or got stuck
with a virus that was dumb enough to move the physical offset of the
partition table in the MBR so the standard bootstrap program cannot load it,
the standard bootstrap program never knows which OS is in a partition (well,
it can by looking at the attributes in each partition table entry of which
there are only 4 because only primary partitions are listed).

It is NOT up to the MBR bootstrap program to load the operating system. All
it does is load whatever is in the first sector in the active-marked
partition! It is up to whatever is in the first sector of the partition to
load the OS in that partition. The MBR boot program is very elementary.
There are some minor changes which results in different byte counts for the
standard boot program that FDISK /MBR puts into the 460-byte area in the MBR
between FDISK provided with Windows 3.1, Windows 95, Windows 98, and Windows
ME, and the bootstrap program put into the MBR by FIXMBR for Windows 2000
and Windows XP, but it is essentially the SAME PROGRAM!

Stop confusing the MBR bootstrap program with the partition's boot program.
They are separate programs. The OS doesn't care which MBR boot program
loaded its own partition boot program into memory and passed control to it.
That is why you can use a simple multiboot manager that usurps the 460-byte
MBR bootstrap program area. It simply gives you the choice of which
partition's boot sector to load to start the OS in that partition without
you having to change which one is marked active. It is up to the OS to put
whatever it wants in its own partition's boot sector to start the process of
loading that OS.

 

Thanks big V. I know what I did. And I know it worked. I did a
fdisk /MBR again last night to prove it.My system booted normally to WinXP.
best wishes..OJ

 

Seems I was in error.... - I asked around a bit, and the first responses (to
your comments) are coming in.....
<quote>
Assuming basic disks, that's basically right. Fixmbr will leave the MBR's NT
disk signature alone, and fdisk could be more preferable if you need to
clear said sig. (though there are less destructive tools to do that) Older
versions of both might have a problem loading boot sectors past the 1024
cylinder.
Also, Fdisk will overwrite the partition table if the end of sector
signature word is missing. Not sure how fixmbr deals with that.

</quote>

So it seems that it 'can' work - but not that it's a good thing to do!

--
Noel Paton (MS-MVP 2002-2006, Windows)


Nil Carborundum Illegitemi
http://www.crashfixpc.com/millsrpch.htm

http://tinyurl.com/6oztj

Please read http://dts-l.org/goodpost.htm on how to post messages to NG's