iii. LFS Target Architectures

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. (Note that a 32-bit distribution can be installed and used as a host system on a 64-bit AMD/Intel computer.)

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:

Architecture Build Time     Build Size
32-bit       239.9 minutes  3.6 GB
64-bit       233.2 minutes  4.4 GB

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.

The default 64-bit build that results from LFS is a pure 64-bit system. That is, it supports 64-bit executables only. Building a multi-lib system requires compiling many 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 basic Linux system. Some of the LFS/BLFS editors maintain a multilib fork of LFS, accessible at https://www.linuxfromscratch.org/~thomas/multilib/index.html. But that's an advanced topic.