| 1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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| 2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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| 3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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| 4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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| 5 | %general-entities;
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| 6 | ]>
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| 7 |
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| 8 | <sect1 id="pre-architecture">
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| 9 | <?dbhtml filename="architecture.html"?>
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| 10 |
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| 11 | <title>LFS Target Architectures</title>
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| 12 |
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| 13 | <para>The primary target architecture of LFS is the 32-bit Intel CPU. If you
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| 14 | have not built an LFS system before, you should probably start with that
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| 15 | target. The 32-bit architecture is the most widely supported Linux system and
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| 16 | is most compatible with both open source and proprietary software.</para>
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| 17 |
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| 18 | <para>On the other hand, the instructions in this book are known to work, with
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| 19 | some modifications, with both Power PC and 64-bit AMD/Intel CPUs. To build a
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| 20 | system that utilizes one of these CPUs, the main prerequisite, in addition to
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| 21 | those on the next few pages, is an existing Linux system such as an earlier LFS
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| 22 | installation, Ubuntu, Red Hat/Fedora, SuSE, or other distribution that targets
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| 23 | the architecture that you have. Also note that a 32-bit distribution can be
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| 24 | installed and used as a host system on a 64-bit AMD/Intel computer.</para>
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| 25 |
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| 26 | <para>Some other facts about 64-bit systems need to be added here. When
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| 27 | compared to a 32-bit system, the sizes of executable programs are slightly
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| 28 | larger and the execution speeds are only slightly faster. For example, in a
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| 29 | test build of LFS-6.5 on a Core2Duo CPU based system, the following statistics
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| 30 | were measured:</para>
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| 31 |
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| 32 | <screen><computeroutput>Architecture Build Time Build Size
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| 33 | 32-bit 198.5 minutes 648 MB
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| 34 | 64-bit 190.6 minutes 709 MB</computeroutput></screen>
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| 35 |
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| 36 | <para>As you can see, the 64-bit build is only 4% faster and is 9% larger than
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| 37 | the 32-bit build. The gain from going to a 64-bit system is relatively
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| 38 | minimal. Of course, if you have more than 4GB of RAM or want to manipulate
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| 39 | data that exceeds 4GB, the advantages of a 64-bit system are substantial.</para>
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| 40 |
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| 41 | <para>The default 64-bit build that results from LFS is considered a "pure"
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| 42 | 64-bit system. That is, it supports 64-bit executables only. Building a
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| 43 | "multi-lib" system requires compiling many applications twice, once for a
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| 44 | 32-bit system and once for a 64-bit system. This is not directly supported in
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| 45 | LFS because it would interfere with the educational objective of providing the
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| 46 | instructions needed for a straightforward base Linux system. You can refer to
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| 47 | the <ulink url="http://trac.cross-lfs.org/">Cross Linux From Scratch</ulink>
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| 48 | project for this advanced topic.</para>
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| 49 |
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| 50 | <para>There is one last comment about 64-bit systems. There are some packages
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| 51 | that cannot currently be built in a "pure" 64-bit system or require specialized
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| 52 | build instructions. Generally, these packages have some embedded 32-bit
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| 53 | specific assembly language instructions that fail when building on a 64-bit
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| 54 | system. This includes some Xorg drivers from <ulink
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| 55 | url="http://www.linuxfromscratch.org/blfs/view/svn/">Beyond Linux From Scratch
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| 56 | (BLFS)</ulink>. Many of these problems can be worked around, but may require
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| 57 | some specialized procedures or patches.</para>
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| 58 |
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| 59 | </sect1>
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| 60 |
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