Re: [Freedos-devel] How does the boot sector know the partition start

[Decheng F. <fan...@gm...>]

Hi,

On Sat, Sep 24, 2011 at 2:16 AM, Eric Auer <e....@jp...> wrote:

>
> As far as I remember, the MS DOS 7.x / Windows 9x boot
> sectors did use it and it is in fact intentional there.
>
> > In a boot sector, you could attempt to use that information; if so,
> > verifying that the byte at address ds:si contains the value 80h (or at
> the
>
> Which is, again as far as I remember, what Win9x did. If you
> really want to know, you can certainly find an annotated list
> of the machine code of that very widespread boot sector ;-)
>
> > very least has the highest bit set; that is, a value >= 80h) helps with
> > finding out whether the MBR supports this "interface". MBRs are expected
> > to relocate to 60:0 or linear 600h, so another verification would be to
> > check that ds:si then points to one of the entries in the partition table
> > copy there.
>
> Not all MBRs do that, but it is yet another popular convention.
>
>
Yes after reading your e-mail, and after re-checking Minix masterboot.s
code, it also keeps SI pointing to the partition table entry. Meanwhile,
another article talking about MS-DOS MBR also mentions this:

http://www.ata-atapi.com/hiwmbr.html

So I guess this is also a convention, or at least a de-facto standard?

Best regards,

Robbie