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[mtools] Re: [fdutils] 3.84MB floppy image with superformat

From: Alain Knaff
Subject: [mtools] Re: [fdutils] 3.84MB floppy image with superformat
Date: Fri, 15 Apr 2005 12:47:40 +0200
User-agent: KMail/1.8

On Friday 15 April 2005 10:27, Rudi Langhanki wrote:
> Background:
> I am using pxelinux (with memdisk) on a linux server to allow some diskless
> clients to boot an MS-DOS boot image from LAN.

First of all, let me point out that this request belongs on the mtools
mailing list rather than fdutils.

Fdutils only deals with *physical* floppies, rather than with floppy
disk images to be downloaded over the network...

Mtools deals with the contents (filesystem) of those images, no matter
whether they are actually on a floppy, or just images on the network.

> This works fine for 1.44MB images.
[... ]
> I tried to increase the values in the mformat command, but the
> resulting image was no longer bootable.

This is due to the heuristics used in memdisk. It assumes that the
image is a hard disk image (with MBR and partitions) if the size
doesn't correspond to a short list of floppy sizes (see

    368,640 bytes    360K floppy   (DD 5.25") 
    737,280 bytes    720K floppy   (DD 3.5") 
  1,222,800 bytes   1200K floppy   (HD 5.25") 
  1,474,560 bytes   1440K floppy   (HD 3.5") 
  1,720,320 bytes   1680K floppy   (HD 3.5" extended format) 
  1,763,328 bytes   1722K floppy   (HD 3.5" extended format) 
  2,949,120 bytes   2880K floppy   (ED 3.5")

Everything else is assumed to be a hard disk.

However, according to the same page, you may override this
autodetection by adding the word "floppy" to the pxe command line that
starts your memdisk boot disk, and also adding c= h= s= parameters for
the geometry (must match those used for mformat) to the same

However, there might still be issues with the BIOS becoming confused
with an unusually "large" floppy drive...

> I tried to use an MBR of an existing HDD and the 8MB DOS-partition,
> not bootable.

If you want to set up a hdd image, you need to use the partition=1
flag in .mtoolsrc. First use fdisk to partition it, then mformat (with
appropriate partition flag) to format the partition you made.

> What am I doing wrong?
> Any help possible?
> At least, do I have the chance to go up to a 3.84MB floppy image? For

With the floppy flag, memdisk should support this. However, as far as
I understand, memdisk heavily relies on the BIOS, so depending on your
machine, it might still give you trouble if the BIOS of your machine
doesn't support it.

> this I did not find any cylinder, sector, head numbers on the web. Do

Use whatever works... It doesn't need to match any format used by
fdutils at all, as we are not dealing with a physical disk here.

> you know the correct settings for such a floppy? And, very important,
> I don't have any high capacity floppy disk drives at hand. I try to create
> a floppy image to use it for boot from lan.
> Thanks for any help.

You don't need any physical floppy drive for this, you can use the
file= parameter in .mtoolsrc to build your directly image in a file on
your hard disk.



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