The primary target architectures of LFS are the AMD/Intel x86_64 (64-bit) CPUs. The instructions in this book are also known to work on 32-bit x86 CPUs with SSE2 support (for example Pentium 4) but not tested with earlier, less-capable 32-bit x86 processors. 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.
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/mlfs/view/dev/. But that's an advanced topic.