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@@ -14,52 +14,37 @@
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and x86_64 (64-bit) CPUs. On the other hand, the instructions in this book are
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also known to work, with some modifications, with the Power PC and ARM CPUs. To
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build a system that utilizes one of these CPUs, the main prerequisite, in
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-addition to those on the next few pages, is an existing Linux system such as an
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+addition to those on the next page, is an existing Linux system such as an
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earlier LFS installation, Ubuntu, Red Hat/Fedora, SuSE, or other distribution
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that targets the architecture that you have. Also note that a 32-bit
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distribution can be installed and used as a host system on a 64-bit AMD/Intel
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computer.</para>
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-<para>Some other facts about 64-bit systems need to be added here. When
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-compared to a 32-bit system, the sizes of executable programs are slightly
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-larger and the execution speeds of arbitrary programs are only slightly faster.
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-For example, in a test build of LFS-6.5 on a Core2Duo CPU based system, the
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-following statistics were measured:</para>
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+<para>For building LFS, the gain of building on a 64-bit system
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+compared to a 32-bit system is minimal.
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+For example, in a test build of LFS-9.1 on a Core i7-4790 CPU based system,
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+using 4 cores, the following statistics were measured:</para>
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<screen><computeroutput>Architecture Build Time Build Size
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-32-bit 198.5 minutes 648 MB
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-64-bit 190.6 minutes 709 MB</computeroutput></screen>
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-
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-<para>As you can see, the 64-bit build is only 4% faster and is 9% larger than
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-the 32-bit build. The gain from going to a 64-bit system is relatively
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-minimal. Of course, if you have more than 4GB of RAM or want to manipulate
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-data that exceeds 4GB, the advantages of a 64-bit system are substantial.</para>
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-
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-<note><para>The above discussion is only appropriate when comparing
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-builds on the same hardware. Modern 64-bit systems are considerably
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-faster than older 64-bit systems and the LFS authors recommend building
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-on a 64-bit system when given a choice.</para></note>
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-
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-<para>The default 64-bit build that results from LFS is considered a "pure"
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-64-bit system. That is, it supports 64-bit executables only. Building a
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-"multi-lib" system requires compiling many applications twice, once for a
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-32-bit system and once for a 64-bit system. This is not directly supported in
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-LFS because it would interfere with the educational objective of providing the
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-instructions needed for a straightforward base Linux system. You can refer to
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-the <ulink url="http://trac.clfs.org/">Cross Linux From Scratch</ulink>
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-project for this advanced topic.</para>
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-
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-<!-- This does not appear to be valid for LFS/BLFS any more
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-<para>There is one last comment about 64-bit systems. There are some older
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-packages that cannot currently be built in a "pure" 64-bit system or require
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-specialized build instructions. Generally, these packages have some embedded
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-32-bit specific assembly language instructions that fail when building on a
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-64-bit system. This includes some Xorg drivers for some legacy video cards at
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-<ulink url="http://xorg.freedesktop.org/releases/individual/driver/">
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-http://xorg.freedesktop.org/releases/individual/driver/</ulink>. Many of these
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-problems can be worked around, but may require some specialized procedures or
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-patches.</para>
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--->
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+32-bit 239.9 minutes 3.6 GB
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+64-bit 233.2 minutes 4.4 GB</computeroutput></screen>
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+
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+<para>As you can see, on the same hardware, the 64-bit build is only 3% faster
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+and is 22% larger than the 32-bit build. If you plan to use LFS as a LAMP
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+server, or a firewall, a 32-bit CPU may be largely sufficient. On the other
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+hand, several packages in BLFS now need more that 4GB of RAM to be built
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+and/or to run, so that if you plan to use LFS as a desktop, the LFS authors
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+recommend building on a 64-bit system.</para>
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+
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+<para>The default 64-bit build that results from LFS is considered a
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+<quote>pure</quote> 64-bit system. That is, it supports 64-bit executables
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+only. Building a <quote>multi-lib</quote> system requires compiling many
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+applications twice, once for a 32-bit system and once for a 64-bit system.
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+This is not directly supported in LFS because it would interfere with the
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+educational objective of providing the instructions needed for a
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+straightforward base Linux system. Some LFS/BLFS editors maintain a fork
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+of LFS for multilib, which is accessible at <ulink
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+url="http://www.linuxfromscratch.org/~thomas/multilib/index.html"/>. But it
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+is an advanced topic.</para>
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</sect1>
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-
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Pierre Labastie