Trunk is now identical to Testing

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@4648 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

1 files changed, 39 insertions, 1 deletions

diff --git a/chapter04/aboutsbus.xml b/chapter04/aboutsbus.xml
index d99ac1f0f..34e1a1ef4 100644
--- a/chapter04/aboutsbus.xml
+++ b/chapter04/aboutsbus.xml
@@ -7,6 +7,44 @@
 <title>About SBUs</title>
 <?dbhtml filename="aboutsbus.html"?>
 
-<para>See testing</para>
+<para>Many people would like to know beforehand approximately how long
+it takes to compile and install each package. Because Linux From
+Scratch can be built on many different systems, it is impossible to
+provide accurate time estimates.  The biggest package (Glibc) will
+take approximately 20 minutes on the fastest systems, but could take
+up to three days on slower systems! Instead of providing actual times,
+the Static Build Unit (SBU) measure will be
+used instead.</para>
+
+<para>The SBU measure works as follows. The first package to be compiled
+from this book is the statically-linked Binutils in <xref
+linkend="chapter-temporary-tools"/>.  The time it takes to compile
+this package is what will be referred to as the Static Build Unit
+or SBU. All other compile times will be expressed relative to this
+time.</para>
+
+<para>For example, consider a package whose compilation time is 4.5
+SBUs. This means that if a system took 10 minutes to compile and
+install the static Binutils, it will take
+<emphasis>approximately</emphasis> 45 minutes to build this example
+package. Fortunately, most build times are shorter than the one
+for Binutils.</para>
+
+<para>Please note that if the system compiler on the host is GCC-2.x based, the
+SBUs listed may be somewhat understated. This is because the SBU is
+based on the very first package, compiled with the old GCC, while the
+rest of the system is compiled with the newer GCC-&gcc-version; (which is
+known to be approximately 30 percent slower). SBUs are also not
+highly accurate for Symmetric Multi-Processor (SMP)-based machines.</para>
+
+<para>To view actual timings for a number of specific machines, we recommend
+<ulink url="&lfs-root;~bdubbs/"/>.</para>
+
+<para>In general, SBUs are not very accurate because they depend on many
+factors, not just the GCC version. They are provided
+here to give an estimate of how long it might take to
+install a package, but the numbers can vary by as much as dozens of
+minutes in some cases.</para>
 
 </sect1>
+