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From: Bjorn Simonsen <soabs AT hermes DOT svf DOT uib DOT no>
To: opendos AT mail DOT tacoma DOT net
Date: Sat, 15 Feb 1997 16:35:14 +0100
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Subject: [opendos] Re: OpenDOS multi-boot success story
Reply-to: Bjorn DOT Simonsen AT aorg DOT uib DOT no
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On 10 Feb 97, Weiqi Gao <weiqigao AT crl DOT com> wrote

> While we are on the topic of MBRs and dual boots, I would like to make
> things clearer.  It is my impression that:
> 1. The A:\> sys a:\ c: command run from a MS DOS 6.22 or OpenDOS 7.01 boot
> floppy will do the following:
>     Copy the three system files to C:\
>     Write the MBR.
> 2. The FDISK /MBR command will write the MBR to C:\.
> If the above impressions are true, then I think I've got the answer to
> multi booting MS DOS, OpenDOS and Linux with grub 0.4.  The trick is to
> write the MS DOS and OpenDOS MBRs to DOS files with the DEBUG command, and
> have grub boot off the files:
> 
> C:\> DEBUG
> -l 100 2 0 1
> -rcx
> CX 0000
> :200
> -n MSDOS.MBR
> -w 100
> Writing 00200 bytes
> -q
> 
> This will write the MBR on the C drive to the file MSDOS.MBR.  You can then
> write the OpenDOS MBR to OPEMDOS.MBR after running SYS from the OpenDOS
> boot floppy.
> 
> To boot from a file instead of the MBR, you only need to change the 
>     chainloader=+1
> line to something like
>     chainloader=(hd0, 1)/msdos.mbr
> for the MS DOS boot stanza.  Similarly for OpenDOS and Linux.
> 
> Since grub have knowledge of the FAT and ext2fs file systems, it will find
> the MBRs and the Linux kernel file, and boot from there.
> 
> I haven't tried this yet, but I believe this will work.

(sorry for the long quote, I didn't know where to snip :-) 

Has anyone else tried it? I've read several postings about the Grub
bootmanager -  and the above method spells ingenuity  to me!  
But, is it safe (the debug script)? If not, does anyone  know if there 
is any software (free/sharew) available which will perform this saving 
of MBR to file? If the above method is safe, how does one reverse the 
process, if ever needed?  I guess I can't use Grub when I use disk 
compression? Still, I would appreciate any information and pointers 
about this, since among other things I would like to be able to copy 
the MBR to a file and then use a file comparison utility at boot time - 
to check the boot sector for changes - kind of a integrity check 
against boot virus. Also,  I guess I will be using Grub later, so, 
anyway - suggestions appreciated.  Anyone? 
 

Thanks, 

Bjorn
-learning




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