Re: Undersanding bootable media
Marlon Urias: 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. Yes. But dos floppies boot just fine by making copies of other dos boot disks. That's because every DOS floppy has a valid boot sector on it. Try looking at the first sector of a DOS floppy (umount /dev/fd0; less -f /dev/fd0). Daniel J. Brosemer: ... (I'm not real clear on whether floppies have an MBR or just Hard Disks do). No, they don't - they just have a Boot Sector. Hard disks have a Boot sector in each partition, so there's a Master Boot Record at the start that decides which of the partitions will be booted. BTW, if you want to play with boot sectors, be aware that DOS in its infinite wisdom keeps drive geometry there. Even when there's a perfectly good partition table nearby, it still takes the data from the Boot sector. 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. No, it's because all DOS-formatted floppies already have a boot sector. Your friend is correct when he says you must use a lowlevel tool. Yup. The DOS boot sector doesn't work for linux. HTH Jiri -- [EMAIL PROTECTED] We'll know the future has arrived when every mailer transparently quotes lines that begin with From , but no-one remembers why.
Re: Re: Undersanding bootable media
Quoting Ries van Twisk ([EMAIL PROTECTED]): The reply given below tells you plenty about how computers boot, but I thought I'd add a couple of points to the original question (and I don't have the original to reply to). 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. Yes, that's right. dd will copy the whole filesystem and the boot sectors. But dos floppies boot just fine by making copies of other dos boot disks. Well, that depends how they are copied. If you take a virgin disk, FORMAT A: and then COPY the files, you won't be able to boot that. But if you copy the files onto a floppy that was formatted in the past to make it bootable by typing, say, FORMAT /S A: then it will remain bootable (also as long as the hidden files have not been deleted). If you use DISKCOPY A: A: to copy a disk, the bootability or otherwise will be transferred from the first disk to the second along with the files. (About the only change is the volume serial number.) This is roughly equivalent to using dd. 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 [snipped the explanation] Cheers, -- Email: [EMAIL PROTECTED] Tel: +44 1908 653 739 Fax: +44 1908 655 151 Snail: David Wright, Earth Science Dept., Milton Keynes, England, MK7 6AA Disclaimer: These addresses are only for reaching me, and do not signify official stationery. Views expressed here are either my own or plagiarised.
Undersanding bootable media
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
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
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 -- Unsubscribe? mail -s unsubscribe [EMAIL PROTECTED] /dev/null 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
