Message-Id: <199702101405.AA03645@mail.crl.com>
From: "Weiqi Gao" <weiqigao AT crl DOT com>
To: "OpenDOS discussion list" <opendos AT mail DOT tacoma DOT net>
Subject: Re: [opendos] OpenDOS multi-boot success story
Date: Mon, 10 Feb 1997 08:06:31 -0600
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mharris AT blackwidow DOT saultc DOT on DOT ca wrote:

>[Dual boot story, ...]

>I couldn't for the life of me figure out how to get DOS
>6.22 to boot though.  I figured that SC needed to somehow capture
>a DOS 6.22 MBR though so I booted clean off of the DOS 6.22
>installation disks and did a SYS C:.  I feared that this might
>cause HD problems or destroy SC, however I tried it anyway.  At
>this point I figured that I'd now be able to set up 6.22 on the
>SC menu and then boot it ok, but that OD probably wouldn't work
>anymore.  Well, upon rebooting, I found out that I was right.

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.

--
Weiqi Gao
weiqigao AT crl DOT com