Re: what is an image

Thanks very much to Martin Stricker. I have better understanding now. But 
i think i have to read it more times :-) Once again, thank you.

Soli Deo Gloria & Sola Christa Eterna
Hendra/EL-00

On Sun, 17 Jul 2005, Martin Stricker wrote:

> 13200178 Hendra Tampang Allo wrote:
>>
>> Hi friends, i am sorry i am a newbie. I still don't understand what
>> image means.For example, what does boot image mean?
>
> In this case, it means an image of a filesystem. It is a file which
> contains the whole structure and files of a complete filesystem. On
> Unix-like operating systems (like Linux) you can look into it (and even
> change the content!) by mounting it onto the loopback device (notz to be
> confused with the loopback interface which is the computer's own network
> interface and always has the IP address 127.0.0.1). Look at "man mount"
> and search for the option -o loop.
>
> Filesystem images are mostly used for bootable media, because to be
> bootable the filesystem on the bootable media (floppy, harddisk, CD
> etc.) needs to have a bootloader in its master boot record (MBR). The
> MBR is a special place and cannot be written with normal methods (it is
> not accessible by normal programs). That means: If you make a copy of
> all files from a bootable floppy to a blank floppy, that copied floppy
> is *not* bootable - the MBR has not been copied (and even if the boot
> would fail, because the location of the files on the floppy are not
> identical - booting is quite complicated and difficult). So the easiest
> way to send bootable meadia is to create an image of the filesystem,
> because that is an *exact* copy of everything including the MBR, and
> everything stays at exactly the same place.
>
> Most commonly you will see floppy images and ISO images, the latter are
> either for CDs or DVDs (depending on the size). As a side note, every
> bootable CD and DVD contains a bootable floppy image, because for
> booting the CD/DVD drive acts like a floppy drive (that was easier to
> implement than to invent a new way of booting). So if you want to create
> a bootable CD, you need a bootable floppy image and tell your CD burning
> software about it (on Linux it is mkisofs -b option, and mkisofs creates
> an ISO image).
>
> To write a boot image onto a floppy, you can use dd on Linux or rawrite
> on Windows. To write an ISO image onto a CD or DVD you need to tell your
> burning software that you want to burn an image. You cannot write an
> image as a file to a medium, because it's not a file but a filesystem.
>
> I hope that helps and is not too complicated!
>
> Best regards,
> Martin Stricker
> -- 
> Homepage: http://www.martin-stricker.de/
> Linux Migration Project: http://www.linux-migration.org/
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>
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