Changes in prologue/architecture.xml [e43d96fa:7152faa]

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• prologue/architecture.xml (modified) (2 diffs)

prologue/architecture.xml

@@ -11 +11 @@
   <title>LFS Target Architectures</title>
 
-<para>The primary target architectures of this LFS edition are the little
-endian MIPS64 release 2 to 5 CPUs (the release 6 is not backward-compatible
-with earlier releases).  On the other hand, the instructions
-in this book are also known to work, with some modifications, for
-MIPS CPUs with a different byte order, word size, or ISA version.  To
+<para>The primary target architectures of LFS are the AMD/Intel x86 (32-bit)
+and x86_64 (64-bit) CPUs.  On the other hand, the instructions in this book are
+also known to work, with some modifications, with the Power PC and ARM CPUs. To
 build a system that utilizes one of these alternative CPUs, the main prerequisite, in
 addition to those on the next page, is an existing Linux system such as an
 earlier LFS installation, Ubuntu, Red Hat/Fedora, SuSE, or some other distribution
-that targets that architecture.</para>
+that targets that architecture. (Note that a 32-bit
+distribution can be installed and used as a host system on a 64-bit AMD/Intel
+computer.)</para>
 
-<para>There are three widely-used ABIs for 64-bit MIPS programs.
-The <quote>o32</quote> ABI is compatible with the ABI of the legacy 32-bit
-MIPS programs and it's used for running those legacy 32-bit programs on a
-64-bit MIPS CPU.  The <quote>n64</quote> ABI is designed for taking the full
-advantage of 64-bit capability.  The <quote>n32</quote> ABI is similar to
-n64 but using 32-bit pointers, mainly used for 64-bit devices with a small
-amount of RAM. The default 64-bit build that results from LFS is a
-<quote>pure</quote> n64 system. That is, it supports n64 executables
+<para>The gain from building on a 64-bit system, as
+compared to a 32-bit system, is minimal.
+For example, in a test build of LFS-9.1 on a Core i7-4790 CPU based system,
+using 4 cores, the following statistics were measured:</para>
+
+<screen><computeroutput>Architecture Build Time     Build Size
+32-bit       239.9 minutes  3.6 GB
+64-bit       233.2 minutes  4.4 GB</computeroutput></screen>
+
+<para>As you can see, on the same hardware, the 64-bit build is only 3% faster
+(and 22% larger) than the 32-bit build. If you plan to use LFS as a LAMP
+server, or a firewall, a 32-bit CPU may be good enough. On the other
+hand, several packages in BLFS now need more than 4 GB of RAM to be built
+and/or to run; if you plan to use LFS as a desktop, the LFS authors
+recommend building a 64-bit system.</para>
+
+<para>The default 64-bit build that results from LFS is a
+<quote>pure</quote> 64-bit system. That is, it supports 64-bit executables
 only. Building a <quote>multi-lib</quote> system requires compiling many
-applications multiple times, each time for an ABI to be supported.
+applications twice, once for a 32-bit system and once for a 64-bit system.
 This is not directly supported in LFS because it would interfere with the
 educational objective of providing the minimal instructions needed for a
@@ -36 +46 @@
 of LFS, accessible at <ulink
 url="https://www.linuxfromscratch.org/~thomas/multilib/index.html"/>. But
-it's for x86_64, and anyway multilib is an advanced topic.</para>
+that's an advanced topic.</para>
 
 </sect1>