[syslinux] Memdisk/floppy image question

[ganapathy murali krishnan]

I need to create a DOS image larger than the usual 2.88MB. I can't use a
hard disk image (since I want the real hard disk to be called C:). I am 
trying to use a 9MB floppy image. My question is related to the process 
of creating such an image. Here is what I did.

* Create a file of size 9MB.
* Use losetup, format it using FAT filesystem.
* Copy all the files I want (IO.SYS,....)
* dd the first 512 bytes from a 2.88MB floppy image to the new file.
* Compress the file.

Finally at the boot prompt I did

boot: memdisk initrd=dosimage.img floppy image=shell

(Ignore the image=shell part, I am passing arguments).

* Isolinux decompresses the file without any errors.
* Disk is floppy, 9216K C/H/S 4/122/37 (size is correct)
* Reports an error "INT 13 08: Assuming this is the only drive"
   There is no floppy drive on this system, so the assumption is valid.
* Finally it prints "loading boot sector...booting..."

At this point I guess control has been transferred to the boot sector of 
the floppy image. Immediately I see a "Invalid System Disk... Replace 
the disk and continue..." error.

If I am right the problem is in the creation of the floppy image. More 
specifically, the boot sector. I think the boot sector needs to be 
modified somehow to tell DOS, about the geometry of the non-standard 
floppy image. How do I go about doing it? Is there any utility that will 
do it for me, like mkdiskimage does for hard disk?

- Murali