Kernel cares where it should reside?

[Yedidyah Bar-David]

On Thu, Apr 02, 2009 at 12:32:53PM +0300, David Harel wrote:
> Hi there,
>
> Using Gentoo (and have to configure kernel).
> When I do the command - file - on kernel file I just built it says,  
> among other things, root_dev 0x801.
> The working kernel says - root_dev 0x10.
> Where is this parameter determined

Not sure exactly, somewhere in the build process. You can change it with
'rdev', but you do not need to:

> and since when does the kernel care  
> where it resides?

It's not 'since', but 'until when'. It was so since the very beginning.
The kernel had a small boot loader in its start. You could 'cat zImage >
/dev/fd0' and get a bootable floppy. No standard boot loader (lilo,
grub) care{s,ed} about this. IIRC today it does not work anymore,
perhaps never worked with bzImage.
The reason it cared is obvious - you had to tell it which FS to mount as
root. And had no config file to write 'root=something'.
-- 
Didi