Multilib
Enabling the [multilib] repository allows the user to run and build 32-bit applications on 64-bit installations of Arch Linux. [multilib] creates a directory containing 32-bit instruction set libraries inside /usr/lib32/, which 32-bit binary applications may need when executed.
To use the [multilib] repository, uncomment the following from /etc/pacman.conf:
[multilib] Include = /etc/pacman.d/mirrorlist
You will then need to update the package list by running pacman with the -Sy switch.
Directory structure
A 64-bit installation of Arch Linux with [multilib] enabled follows a directory structure similar to Debian. The 32-bit compatible libraries are located under /usr/lib32/, and the native 64-bit libraries under /usr/lib/.