GRUB discussion follow up ?

[Jacques B.]

On 10/21/07, William Case <billlinux at rogers.com> wrote:
> Hi;
>
> As a result of the ongoing GRUB discussion, I have been trying to trace
> the use of GRUB from BIOS to the end of GRUB stage 2.  I am particularly
> interested in seeing how the MBR is used.
>
> I can create a temporary copy of my MBR using:
> # dd if=/dev/sdX of=/tmp/sda-mbr.bin bs=512 count=1
>
> My question is; what program should I use to read this file in a human
> meaningful way (hexdump??)?  I am trying to see how the MBR names
> partitions; and how GRUB uses those names.  That is, are the partitions
> named in MBR actually named hd0,0 (ie the binary or hex equivalent of
> hd0,0) etc. or is there a further translation step required by GRUB?
> Does the device/partitioning system used by MBR and GRUB have a name(s)?
> (For Internet search purposes).
>
> I am interested in the hardware/software interface of booting.  Is there
> anything additional I should know about this partition-locating process?
>
> --
> Regards Bill
>
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I simply pipe dd to xxd.
dd {......} | xxd

And as Robert indicated, the 512 bytes is broken down as MBR for 446
bytes, 64 bytes for partition table (4 X 15), and 2 byte magic number
\x55\xaa.  I spent a bit of time last Spring trying to figure out
where in the MBR code was the info telling it where to get stage 1.5.
I didn't spend any real significant time on it seeing it was way
beyond what I had to understand so dropped it due to lack of time.  If
you figure out that info I'd be interested.

Jacques B.