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>5.11. Disks without filesystems</H1
><P
>Not all disks or partitions are used as filesystems.
A swap partition, for example, will not have a filesystem on it.
Many floppies are used in a tape-drive emulating fashion, so that a
<B
CLASS="COMMAND"
>tar</B
> (tape archive) or other file is written
directly on the raw disk, without a filesystem. Linux boot floppies
don't
contain a filesystem, only the raw kernel.</P
><P
>Avoiding a filesystem has the advantage of making more of
the disk usable, since a filesystem always has some bookkeeping
overhead. It also makes the disks more easily compatible with other
systems: for example, the <B
CLASS="COMMAND"
>tar</B
> file format is the
same on all systems, while filesystems are different on most
systems. You will quickly get used to disks without filesystems if
you need them. Bootable Linux floppies
also do not necessarily have a filesystem, although they may.</P
><P
>One reason to use raw disks is to make image copies of them.
For instance, if the disk contains a partially damaged filesystem,
it is a good idea to make an exact copy of it before trying to fix
it, since then you can start again if your fixing breaks things even
more. One way to do this is to use <B
CLASS="COMMAND"
>dd</B
>:
<TABLE
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><TR
><TD
><FONT
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><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>$</TT
> <TT
CLASS="USERINPUT"
><B
>dd if=/dev/fd0H1440
of=floppy-image</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>2880+0 records in
2880+0 records out</TT
>
<TT
CLASS="PROMPT"
>$</TT
> <TT
CLASS="USERINPUT"
><B
>dd if=floppy-image
of=/dev/fd0H1440</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>2880+0 records in
2880+0 records out</TT
>
<TT
CLASS="PROMPT"
>$</TT
>
</PRE
></FONT
></TD
></TR
></TABLE
>
The first <B
CLASS="COMMAND"
>dd</B
> makes an exact image of the floppy
to the file <TT
CLASS="FILENAME"
>floppy-image</TT
>, the second one writes
the image to the floppy. (The user has presumably switched the
floppy before the second command. Otherwise the
command pair is of doubtful usefulness.)</P
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