Rewording the SBUs section.

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@2719 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

chapter02/aboutsbus.xml

@@ -2,28 +2,29 @@
 <title>About SBUs</title>
 <?dbhtml filename="aboutsbus.html" dir="chapter02"?>
 
-<para>SBUs are <emphasis>Static Bash Units</emphasis> and they are our way
+<para>Most people would like to know beforehand how long it approximately
-of identifying how long a package takes to compile. Why don't we use normal
+takes to compile and install each package. But "Linux from Scratch" is built
-times like anybody else?</para>
+on so many different systems, it is not possible to give actual times that are
+anywhere near accurate: the biggest package (Glibc) won't take more than
+twenty minutes on the fastest systems, but will take something like three days
+on the slowest -- no kidding. So instead of giving actual times, we've come up
+with the idea of using the <emphasis>Static Binutils Unit</emphasis>
+(abbreviated to <emphasis>SBU</emphasis>).</para>
 
-<para>The biggest problem is that times cannot be accurate, not even a
+<para>It works like this: the first package you compile in this book is the
-little bit. So many people install LFS on so many different systems, the
+statically linked Binutils in Chapter 5, and the time it takes to compile this
-times it takes to compile something varies too much. One package may take
+package is what we call the "Static Binutils Unit" or "SBU". All other compile
-20 minutes on one system, but that same package may take 3 days on another
+times will be expressed relative to this time.</para>
-(this is not an exaggeration). So instead we've come up with a
-<emphasis>Static Bash Unit</emphasis> or <emphasis>SBU</emphasis>.</para>
 
-<para>It works like this: the very first package you compile in this book
+<para>For example, the time it takes to build the static version of GCC is 3.9
-is Bash in Chapter 5 and it'll be statically linked. The time it takes to
+SBU. This means that if on your system it took 10 minutes to compile and
-compile this package will be the basis and called the SBU. All other
+install the static Binutils, then you know it will take nearly 40 minutes to
-compile times are relative to the time it takes to install Bash. For
+build the static GCC. Fortunately, most build times are much shorter than the
-example, GCC-3.2 takes about 9.5 SBUs and it's proven that this number is
+one of Binutils.</para>
-fairly consistent among a lot of different systems. So multiply 9.5 by the
-number of seconds it takes for Bash to install (the SBU value) and you get
-a close approximation of how long GCC will take on your system.</para>
 
-<para>Note: We've seen that SBUs don't work well on SMP based machines. So
+<para>Note that SBUs don't work well for SMP-based machines. But if you're so
-all bets are off if you're lucky enough to have an SMP setup.</para>
+lucky as to have multiple processors, chances are that your system is so fast
+that you don't mind.</para>
 
 </sect1>