Re: [gentoo-user] [gentoo-amd64] Help! New install and New User to linux - Gentoo!

[Richard Fish]

On 4/20/06, Jarry <jarry@×××.net> wrote:
> Richard Fish wrote:
>
> > No. both grub and lilo work through the system BIOS.  Neither can
> > 'see' things not provided through the system BIOS.
>
> Are you absolutely sure about lilo?

Checking the source and the README in the source of 22.7.1 makes it
pretty clear that lilo is still using the BIOS for booting.

> lilo used bios for disk sector read, but I think is not using
> anymore (quite a long time). Thanks to that you can have
> /boot (more exactly, kernel) wherever you want.
>
> int13h is called with following registers:
> AH:                     02h (read sectors from drive)
> CH + 2low bits from CL: cylinder number (0-1023)
> rest 6bits from CL:     sector number (1-63)
> DH:                     head (1-255)
>
> That's the famous "8-GB limit"

You are correct about old systems having a 1024-cylinder limit, but
the solution for this was that the system bios was extended to allow
access to sectors >= 1024.  The typical term for this is the "13h
extensions".  In lilo documentation, this is the "EDD packets".

> "famous"), where you had to install kernel with old lilo to be
> able to boot it. But at least a couple of years there is no such
> a limit with lilo. I think I have read somewhere that lilo is
> not using bios for disk-access anymore. I'll try to dig it out...

This might be true on itanium or other non-x86 platforms (I know
nothing about these).  But on x86, the BIOS controls booting, and the
OS cannot access the disks any other way than through the BIOS until
it's own device drivers are loaded.  So unless lilo has been adding
device drivers for the plethora of SCSI, FC, IDE, SATA, IEEE1284, and
USB disk controllers out there, and making them all fit in the
impossibly small space of the MBR (~460 bytes?), it is using the BIOS
for at least some actions.

-Richard

-- 
gentoo-user@g.o mailing list