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+<?xml version="1.0" encoding="ISO-8859-1"?>
+<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
+  <!ENTITY % general-entities SYSTEM "../general.ent">
+  %general-entities;
+]>
+
+<sect1 id="pre-architecture">
+  <?dbhtml filename="architecture.html"?>
+
+  <title>LFS Target Architectures</title>
+
+<para>The primary target architecture of LFS is the 32-bit Intel CPU.  If you
+have not built an LFS system before, you should probably start with that
+target.  The 32-bit architecture is the most widely supported Linux system and
+is most compatible with both open source and proprietary software.</para>
+
+<para>On the other hand, the instructions in this book are known to work, with
+some modifications, with both Power PC and 64-bit AMD/Intel CPUs.  To build a
+system that utilizes these CPUs, the main prerequsite in addition to those on
+the next few pages, is an existing system such as an earlier LFS system,
+Ubuntu, Red Hat/Fedora, SuSE, or other distribution that targets the system
+that you have.  Also note that a 32-bit system can be installed and used as a
+host system on a 64-bit AMD/Intel system.</para>
+
+<para>If you decide to target a 64-bit AMD/Intel system, LFS does have some
+limitations.  First, it does not currently provide instructions for a 64-bit
+boot loader.  If there is an existing boot loader, it can be used to boot to
+any LFS system you build, but <xref linkend="ch-bootable-grub"/> cannot be
+built on a 64-bit system.</para>
+
+<para>Some other facts about a 64-bit systems need to be added here.  When
+compared to a 32-bit system, the sizes of executable programs are slightly
+larger and the execution speeds are only slightly faster.  For example, in a
+test build of LFS-6.5 on a Core2Duo CPU based system, the following statistics
+were measured:</para>
+
+<screen><computeroutput>Architecture Build Time     Build Size 
+32-bit       198.5 minutes  648 MB 
+64-bit       190.6 minutes  709 MB</computeroutput></screen>
+
+<para>As you can see, the 64-bit build is only 4% faster and is 9% larger than
+the 32-bit build.  The gain from going to a 64-bit system is relatively
+minimal. Of course, if you have more than 4GB of RAM or want to manipulate
+data that exceeds 4GB, the advantages of a 64-bit system are substantial.</para>
+
+<para>The default 64-bit build that results from LFS is considered a "pure"
+64-bit system.  That is, it supports 64-bit executables only.  Building a
+"multi-lib" system requires building many applications twice, once for a 32-bit
+system and once for a 64-bit system.  Currently this is not directly supported
+in the book, but is under consideration for a future release.  In the meantime,
+you can refer to the <ulink url="http://trac.cross-lfs.org/">Cross Linux From
+Scratch</ulink> project for this advanced topic.</para>
+
+<para>There is one last comment about 64-bit systems.  There are some packages
+that cannot currently be built in a "pure" 64-bit system or require specialized
+build instructions.  Generally, these packages have some embedded 32-bit
+specific assembly language instructions that fail when building on a 64-bit
+system.  Examples include the  <ulink
+url="http://www.linuxfromscratch.org/blfs/view/cvs/">Beyond Linux From Scratch
+(BLFS)</ulink> packages Zip and some Xorg drivers. Many of these problems can
+be worked around, but may require some specialized procedures or
+patches.</para>
+
+</sect1>
+