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Re: Bios freaks



Les Mikesell wrote:
> Karl Larsen wrote:
>>    I have heard about enough about what my 1994 bios might or might
>> not be doing to Grub. I WAS surprised when the bios showed correct
>> that I do have two hard drives, one a Master the other a Slave and
>> both having 160GB written just like that in the bios. It is old but it
>> is working fine. You want to blame the problems we are having on our
>> bios.
>>
>>    My FC6 where grub still works fine is using the exact same bios! 8-)
> 
> It is the location on the disk where it has to load the kernel that may
> be a problem for an old bios not the overall size. If you want to find
> out for sure, create a /boot partition in the last 100 megs of your
> drive and see if even fc6 can boot from there.  Otherwise it may just be
> the random location where the kernel and initrd happened to land that
> determines whether or it can be loaded when grub asks bios for those
> sectors.
> 
One sure symptom of this is when the old kernel boots fine, but
trying to boot the updated one gets you an error, and the grub
prompt, instead of booting. It gets to be more fun, because if you
have more then one kernel that boots, and you remove one of them,
and re-install the new kernel, it may boot again. (It depends on
what gets written to where the old kernel and initrd were.)

This is a well documented problem, and has to do with the limits of
the int 13 BIOS call to read the disk. The int13h extension of later
BIOS address this problem. The problem does not bother modern OS's
once they are loaded, because they use their own drivers to access
the drive. But it does bother boot loaders because they use the BIOS
to access the drive, at least for loading themselves, and maybe for
loading the OS.

It has come as a surprise to some people when they filled the disk
enough that the updates get written past the part of the drive where
the BIOS can read, and the update is needed for booting. Have you
even had a Windows system complain about not being able to find a
file at boot, but a directory listing shows that the file is there?
That is caused by the same problem. Giving /boot its own partition
located entirely on the part of the drive the BIOS can access solved
that problem for Linux.

Mikkel
-- 

  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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