lfs-book/chapter04/aboutsbus.xml

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<sect1 id="prepare-aboutsbus">
<title>About SBUs</title>
<?dbhtml filename="aboutsbus.html"?>

<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 Standard 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 Binutils in <xref linkend="chapter-temporary-tools"/>.  The
time it takes to compile this package is what will be referred to as the
Standard 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 first pass of 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>In general, SBUs are not entirely accurate because they depend on many
factors, not just the GCC version. Note that on Symmetric Multi-Processor
(SMP)-based machines, SBUs are even less accurate.  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>

<para>To view actual timings for a number of specific machines, we recommend
The LinuxFromScratch SBU Home Page at <ulink url="&lfs-root;~bdubbs/"/>.</para>

</sect1>