[LinuxBIOS] Question about protect mode?

[Juergen Beisert]

On Tuesday 29 May 2007 04:50, Fu xiayin wrote:
>  Hello,everyone.
> I'm a student, and now my  task is studying Linuxbios.
>
> I'm not very clear about the difference between the protect mode and the
> real mode.

Real mode: 16 bit offsets, address space limited to 20 bit.
Protected mode (or "Linear Flat Mode", see below): 32 bit offsets, address 
space 32 bit

> So I wonder why should Linuxbios turn into protect mode at the very
> beginning.

Try to access your ROM at physical address 0xFFFF0000 in real mode and you 
will "feel" the reason. ;-)

> And is there any difference between protect mode in  Linuxbios and in linux
> kernel.
> If any, what's the main difference?

The mode used in LinuxBIOS is more a 32 bit real mode (called "Linear Flat 
Mode") than a protected mode, because there is no protection at all. Also 
there is no paging and no address translation activated. Every segment starts 
at physical offset 0x00000000 and has a limit of 4GiB (this means: "no 
limit").

Juergen