Re: Undersanding bootable media
At 11:16 AM 7/3/1999 -0800, you 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
>
>
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Most of the time just copy file from one disk to another disk is not enough.
As soon as your computer us booting, the processor is starting at some
point in ROM.
ROM does some checking, calls the BIOS etc. etc. I don't know the exact
procedure of the system anymore because of all these new fancy BIOS types,
PNP etc. etc.
Anyway at some point the computer has determined that it's all up and
running, monitor is
connected, keyboard is connected and decides that it's time to look for
something
to go furter. That's where the bootloader comes in.
The computer read's the first 512 bytes from the very first sector on a HD
or floppy
drive.
That little peace of program is loaded into RAM and started (JMP
RamAddres_of_loaded_512_Bytes)
from this point's it's all upto the bootloader on how to load the file system.
If it was a DOS file system it properly load's the partition table (for a
HD) and seek's
for a bootable partition, that that partion is started at a simular way the
bootloader
is started (for a HD it is done it two stages because in the early day's
there was no
partition table so you can load the filesystem directly).
On how it's done in linux I realy don'y know but this is the general way to
load
a filesystem.
So in short, the must be some sort of a bootload at the first sector of a
media
to load a file system. This is nothing to do with the filesystem itself
(DOS, OS2, NTFS, ext2,
etc, etc (etc is NOT a file system but stands for etcetera) ;-) )
Best Regards,
Ries van Twisk
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