Booting FreeBSD-5.3 from NTLDR

Loren M. Lang lorenl at
Wed Feb 2 01:48:51 PST 2005

On Tue, Feb 01, 2005 at 07:32:07PM +0400, Rakhesh Sasidharan wrote:
> On Tue, 1 Feb 2005 19:04:07 +0400, Rakhesh Sasidharan
> <rakhesh.s at> wrote:
> > On Tue, 1 Feb 2005 04:10:49 -0800, Loren M. Lang <lorenl at> wrote:
> > > I think that you should be able to use boot0 and boot1 as a file once
> > > the apropriate fields are filled in.  When boot0 and boot1 are written
> > > to the disk in their special locations, several bytes of each file are
> > > modified to reflex various paramaters like which disk or partition they
> > > should use.  You should be able to extract them with dd and boot them
> > > externally from my understanding of it.  boot1 is normally written to
> > > the first sector of the partitionthat freebsd is installed on, if that's
> > > the first partition on ur second hard drive then:
> > >
> > > dd if=/dev/ad1s1 of=boot1.img count=1
> > >
> > > will extract the file to boot1.img might NTLDR should be able to use.
> > >
> > > dd if=/dev/ad1 of=boot0.img count=1
> I just tried these again. Same results as when I had used the "bs=512"
> option. Extracting "boot0.img" gets me back to the NTLDR screen;
> extracting "boot1.img" gives me a "Boot Error" message.
> But what you said above gave me an idea. Possibly BootPart modifies
> the extracted bootsectors specially, changing the special parameters
> to enable booting of the second disk from the first? Its a thought ...
> maybe the way these files are written to the disk (from where dd
> extracts them), the special parameters are not such that they can be
> booted from the first disk. But when BootPart extracts the sectors, it
> modifies these parameters, enabling the booting. What say?

bs=512 is the default.  The typical sector size of disk drive is 512
bytes.  This is so engrained right now that even flash memory sticks
have to emulate 512 byte sectors when there is nothing that actually
mandates that for flash chips.

Unless BootPart specifically know about how the freebsd boot loaders
work and how to reconize them, I doubt that it's modifying those
parameters.  Now the last 66 bytes of the MBR stores the partition table
of the hard drive, it's possible that BootPart might try to modify that
as it's not part of the boot loader, but the boot loader uses that

> -- 
> 				-- Rakhesh
> 				   rax at

I sense much NT in you.
NT leads to Bluescreen.
Bluescreen leads to downtime.
Downtime leads to suffering.
NT is the path to the darkside.
Powerful Unix is.

Public Key:
Fingerprint: B3B9 D669 69C9 09EC 1BCD  835A FAF3 7A46 E4A3 280C

More information about the freebsd-questions mailing list