Re: C/H/S from user space

[linux-os (Dick Johnson)]

On Fri, 17 Feb 2006, Nick Warne wrote:

> > So, since Linux doesn't destroy that information remaining in
>> the BIOS tables, I show how to make it available to a 'root' user.
>> Observation over several machines will show that the BIOS always
>> uses the same stuff for large media and, in fact, it has no choice.
>> Basically, this means that the first part of the boot-code, the
>> stuff that needs to be translated to fit into the int 0x13 registers,
>> needs to be below 1024 cylinders, 63 sectors-track, and 256 heads.
>> Trivial... even LILO was able to do that! Once the machine boots
>> past the requirement to use the BIOS services, it's a CHS=NOP.
>
>
> If I am off the mark here, forgive me.
>
> Since I moved exclusively to GNU/Linux 2 years ago, I notice when I
> update kernel I get this:
>
> nick@linuxamd:nick$ sudo /sbin/lilo -v
> LILO version 22.5.9, Copyright (C) 1992-1998 Werner Almesberger
> Development beyond version 21 Copyright (C) 1999-2004 John Coffman
> Released 08-Apr-2004 and compiled at 00:18:50 on May 21 2004.
>
> Warning: LBA32 addressing assumed
> Reading boot sector from /dev/hda2
> Warning: Kernel & BIOS return differing head/sector geometries for device 0x80
>    Kernel: 65535 cylinders, 16 heads, 63 sectors
>      BIOS: 1024 cylinders, 255 heads, 63 sectors
> Warning: Kernel & BIOS return differing head/sector geometries for device 0x81
>    Kernel: 29777 cylinders, 16 heads, 63 sectors
>      BIOS: 1024 cylinders, 255 heads, 63 sectors
>
> Now, from day one I never used the -v option with lilo, but as I get
> more experienced (!) I do now and see the above... I have never
> investigated due to worrying if I start messing with it I will trash
> my disks - as I see all anyway on this disks (and no errors), all
> works great/fast etc.
>
> Is this what is going on here (re this thread?).
>
> Nick
>

Nothing to worry about. If you make lots of new kernels to
try them out, you might wish to use GRUB instead of LILO.

However, once the boot-process gets out of 16-bit mode, it
isn't going to use the 16-bit disk services so it doesn't
care about any of that stuff. C/H/S is just a "key" to get
you through the fact that the 16-bit BIOS puts some minimal
stuff in registers to access the disk.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.15.4 on an i686 machine (5589.53 BogoMips).
Warning : 98.36% of all statistics are fiction.
_


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