Re: mabye simple,but i confused

[guorke <gourke@gmail.com>]

Thanks,I must read it carefully

On 6/16/05, Richard B. Johnson <linux-os@analogic.com> wrote:
> On Thu, 16 Jun 2005, guorke wrote:
> 
> > 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 ?
> > Thanks.
> 
> The IBM 'IPL' (initial program load) address was specified to be
> at 7c00. There was room here for only one "sector", which in the
> early days was 512 bytes. The very first sector, the boot sector,
> was loaded into this address and then execution was started at
> a specified offset so that this boot code could load the rest
> of the operating system. To load the rest of the operating system,
> one needs to move the boot-code to somewhere it won't get
> overwritten by subsequent reads from the disk.
> 
> To load Linux, the boot developers wanted to load code 64k at
> a time. The only address in real-mode, that was guaranteed to
> not be in use, where the boot code could load a whole 64k was
> at 90000 hex. This provides a buffer from which the boot-loader
> can copy 64k at a time into the protected-mode address space
> starting at 0x00100000. The boot-loader uses real-mode BIOS
> services to copy the code to the 1 megabyte address which can't
> be reached in real mode.
> 
> Cheers,
> Dick Johnson
> Penguin : Linux version 2.6.11.9 on an i686 machine (5537.79 BogoMips).
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