Message-Id: <199702152000.AA16569@mail.crl.com>
From: "Weiqi Gao" <weiqigao AT crl DOT com>
To: <opendos AT mail DOT tacoma DOT net>
Subject: Re: [opendos] Re: OpenDOS multi-boot success story
Date: Sat, 15 Feb 1997 14:02:15 -0600
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Bjorn Simonsen <soabs AT hermes DOT svf DOT uib DOT no> wrote:

>On 10 Feb 97, Weiqi Gao <weiqigao AT crl DOT com> wrote

>> 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:\.

I'm not sure if the above is right.  SYS doesn't change the MBR, but the
boot sector of the partition (?).

>> C:\> DEBUG
>> -l 100 2 0 1
>> -rcx
>> CX 0000
>> :200
>> -n MSDOS.MBR
>> -w 100
>> Writing 00200 bytes
>> -q

The script is safe, as it only writes to a file.  Nothing else is changed
on the disk.

>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)?

Installing grub will change the MBR of the disk.  But FDISK /MBR (or LILO)
will undo it.  So it's safe in that respect.

>If not, does anyone  know if there 
>is any software (free/sharew) available which will perform this saving 
>of MBR to file?

System Commander can do it for you (and more, like boot to Windows 95 AND
DOS, which is impossible in grub, as Windows 95 and DOS both use IO.SYS and
MSDOS.SYS).

>If the above method is safe, how does one reverse the 
>process, if ever needed?

FDISK /MBR will undo grub.

>I guess I can't use Grub when I use disk 
>compression?

I would think you can, you need to put the boot sector files in the
uncompressed portion (host drive) of the drive.  Disk compression kicks in
later.

>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? 

Get grub from http://www.uruk.org/grub and check out everything yourself.

--
Weiqi Gao
weiqigao AT crl DOT com