Re: Booting with an "extended" floppy

[Thierry Laronde]

On Mon, Feb 05, 2001 at 02:12:45PM +0100, Jochen Hoenicke wrote:
> On Feb 2, Thierry Laronde wrote:
> > On Fri, Feb 02, 2001 at 05:08:50PM +0100, Thierry Laronde wrote:
> > > 
> > > There is a part of a floppy that is lost because
> > > of the formatting informations. Roughly, the "real" size of the media is
> > > 2MB. 
> > 
> > This formulation is, at best, ambiguous. In fact, the 1440 Ko come from
> > the 2 * 80 *18 *512 of the physical formatting. From these 1440 Ko a part
> > is lost with logical formatting (file system). So, without fs you can
> > use the whole 1440 Ko for data.
> 
> You can't get completely rid of the formatting, since the floppy
> controller depends on it.  AFAIK for extended format disks the gap
> between sectors is made shorter so that more sectors can fit on a
> track.

For the ones interested, there are explanations in the info files of the
fdutils suit.
> 
> > But physically, floppy readers and floppies can allow almost 1840 Ko by
> > playing not with heads (there are two), but number of tracks and
> > sectors. The problem is that, by default, BIOS finds the information
> > about floppy in the DDPT, where only "standard" formats are put.
> 
> AFAIK the BIOS doesn't really care about the number of cylinders,
> heads and sectors.  So as long as grub knows how many cylinders and sectors
> the floppy has it should work.  As Okuji wrote I have a patch to read
> the geometry from the BPB of the disk.

Yes, the problem, finally, is to allow GRUB to have (the sooner the better)
the information about the geometry. There are probably some different
solutions (for example, formatting floppy with 23 sectors per track, but
using only the first 18 ones to put the GRUB, and then giving it the info in
order it can access the remainding 5 for the tracks it used, and the whole
tracks for kernel, initrd etc...).

> 
> I have updated my bpb patch and put it to 
>       http://www.informatik.uni-oldenburg.de/~delwi/grub 
> It is almost completely untested.  It compiles for me and runs under
> VMWare, but I can't test all features here.

Thanks, I will try the solution :)
-- 
Thierry LARONDE, Centre de Ressources Informatiques, Archamps - France
http://www.cri74.org
PingOO, serveur de com sur distribution GNU/Linux: http://www.pingoo.org