Re: Booting with an "extended" floppy

[Jochen Hoenicke]

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.

> 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.

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.

To setup an extended format disk, you should format it with mformat,
so that it contains a valid bpb (part of the first sector of a FAT
disk).  Then invoke the grub shell and run setup or install with the
--force-bpb flag.

  Jochen