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<H2><A NAME="SECTION00572000000000000000">Extended and logical partitions</A></H2>
<P>
The original partitioning scheme for PC hard disks allowed
only four partitions. This quickly turned out to be too little
in real life, partly because some people want more than four
operating systems (Linux, MS-DOS, OS/2, Minix, FreeBSD, NetBSD, or
Windows/NT, to name a few), but primarily because sometimes it
is a good idea to have several partitions for one
operating system. For example, swap space is usually best put
in its own partition for Linux instead of in the main
Linux partition for reasons of speed (see below).
<P>
To overcome this design problem, <b>extended partitions</b> were
invented. This trick allows partitioning a <b>primary
partition</b> into sub-partitions. The
primary partition thus subdivided is the extended partition; the
subpartitions are <b>logical partitions</b>. They behave
like primary<A NAME="tex2html17" HREF="footnode.html#1120"><IMG ALIGN=BOTTOM ALT="gif" SRC="./foot_motif.gif"></A> partitions, but are created
differently. There is no speed difference between them.
<P>
The partition structure of a hard disk might look like that in
figure <A HREF="node37.html#figharddisklayout">4.2</A>. The disk is divided into
three primary partitions, the second of which is divided into
two logical partitions. Part of the disk is not partitioned at
all. The disk as a whole and each primary partition has a boot
sector.
<P>
<P><A NAME="1126"> </A><A NAME="figharddisklayout"> </A><IMG WIDTH=281 HEIGHT=276 ALIGN=BOTTOM ALT="figure1122" SRC="img5.gif"><BR>
<STRONG>Figure 4.2:</STRONG> A sample hard disk partitioning.<BR>
<P><BR> <HR>
<P><ADDRESS>
<I>Lars Wirzenius <BR>
Sat Nov 15 02:32:11 EET 1997</I>
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