Re: mabye simple,but i confused

From: guorke
Date: Thu Jun 16 2005 - 03:57:53 EST

yes, give me a lot of help! Thanks

On 6/16/05, DervishD <lkml@xxxxxxxxxxxx> wrote:
> * guorke <gourke@xxxxxxxxx> dixit:
> > in understangding the linux kernel, the authors says
> > "..Moves itself from address 0x00007c00 to address 0x00090000.."
> >
> > What i confused is why the Boot Loader do this, i asked google,but
> > still no answe.
> > who can make me understand it ?
> Well, let's start with the Master Boot Record. In PC's the BIOS
> loads the MBR at address 0x7c00, but the MBR is responsible for
> loading the OS bootsector, if any. And the bootsectors are written
> assuming that they're loaded by a MBR or *by the BIOS itself* so the
> address they assume is 0x7c00. But the MBR is already at that
> address! What can it do? Well, it moves itself out of the place.
> The problem is that the kernel itself could be loaded directly by
> the BIOS (a long time ago, it was possible to boot from a raw floppy
> containing an image of the kernel), and the first sector would be
> loaded at 0x7c00, so the bootsector, MBR, loader or whatever has to
> move out of that address at the very beginning. Why the physical
> address 0x00090000 was used? I don't know. Well, it's well at the top
> of the 640k base memory and the segment starts with 1001 in binary,
> which is a fancy number XDD
> Hope that helps.
> Raúl Núñez de Arenas Coronado
> --
> Linux Registered User 88736 |
> &
> It's my PC and I'll cry if I want to...
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