Re: Undersanding bootable media
On Sun, 7 Mar 1999, Marlon Urias wrote:
> In my quest to understand booting/LILO/MBR's I've come a cross
> a phenomenon I dont understand. Friend of mine (linux guru-ish)
> said that to make a linux bootable floppy you had to use a lowlevel
> tool like dd as opposed to just copying the files over to the floppy.
> But dos floppies boot just fine by making copies of other dos boot disks.
> BUT I tried to copy the files from a dos boot disk onto an CDR, and guess
> what? It wont boot. Despite the fact that it contains the exact same files
> as the floppy. I understand that in order for media to be bootable it's
> MBR needs to contain a "program" to point to the OS, so how does a copied
> dos-boot disk work? Thanks, marlon
Long answer: cp and even the DOS COPY look for a filesystem on the disk
that they are copying from. Their arguments are files. The MBR and the
Boot Sector are not files, and as such are not visible when you are
looking at the disk as a filesystem. When you say that you can copy DOS
disks and they are bootable, I would assume you are using a lowlevel tool
like DISKCOPY. AFAIK this just does the equivalent of a dd into RAM,
pauses for you to change floppies and dd's the image back onto the other
floppy. In order to make a bootable CD-R, you need to have an "image" of
a boot floppy (one file) which contains an MBR(maybe) and a boot sector
(I'm not real clear on whether floppies have an MBR or just Hard Disks
do).
Short answer: There are non-files which are important and I would guess
that you are using a lowlevel tool in DOS without knowing it. Your friend
is correct when he says you must use a lowlevel tool.
HTH.
-Dano
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