Re: Dual Boot Restore

From: hawk (hawk_at_spamex.com)
Date: 05/05/04 

Date: Wed, 05 May 2004 14:05:55 -0700

Many thanks Dan and Patti! Everything now makes sense. And I completed
   Doug's fixboot procedure and everything is back to normal. I didn't
need to use the debug stuff because I had followed a MS procedure for
making a WinXP "boot" floppy before I formatted "C". So, I had the
four files for the root of "C", boot.ini, bootsect.dos, ntldr and
ntdetect.com. Booting with my WinXP CD and following Doug's procedure
went without a problem.

Regards, hawk

Patti MacLeod wrote:
> The very first 512 bytes on a hard drive contains the MBR.......this is
> located prior to C, D or any other logical drives. The debug command reads
> the first sector of "C" drive, not the first sector of the hard drive.
>
> It is my understanding that when the Linux Loader (LILO) is written, and one
> opts to write it to the MBR (as you can have LILO written to the MBR or to
> the boot sector of the partition on which Linux will be installed), the
> loader overwrites the first 4xx (I know it overwrites an amount in the four
> hundred range, I just don't know exactly the amount) bytes of the
> "DOS-style" (for lack of better terminology) MBR with its own code. Thus
> everything but the partition table and signature bytes is overwritten by
> LILO. That was why you had to restore the DOS-style MBR, by running fdisk
> /mbr, when you ditched Linux. The DOS-style MBR doesn't know if there is
> WIN9x or WINNT-style boot code written in any of the boot sectors of any of
> the partitions.....it examines the partition table to find an active,
> bootable partition, loads that partition's boot sector into memory, verifies
> the signature bytes at the end of that partition, then passes control over
> to the boot sector of that partition.
>
> When you formatted and reinstalled 98, it overwrote, without saving it
> anywhere, the NT-style boot code required to boot into XP. This is because
> WIN9x doesn't understand dual boot. XP, however, does understand dual boot,
> and that is why, when it is being installed in a dual-boot situation, it
> saves the WIN9x-style boot code as bootsect.dos before it overwrites the
> boot sector with its own code. I believe the same thing would happen with
> the NT-style boot code if you simply used the fixboot command from Recovery
> Console, without first saving the WIN9x-style code to bootsect.dos The
> NT-style boot code would overwrite the 9x-style code without saving it
> first, rendering XP bootable but not 98.
>
> Another, allbeit far more lengthy, method of repairing your dual boot setup
> would be to perform a repair (in place upgrade) install of XP, as described
> here:
> http://michaelstevenstech.com/XPrepairinstall.htm
> The drawback of the above method would be that you would have to reinstall
> all updates and service packs that you had previously installed. All other
> application data plus user settings would be saved.
>
> I don't know if I've helped to clear up the confusion or make things worse.
> I hope the former.
>
>
>
> Regards,
>

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