Start64!Canonical engineer Josh Powers posted a message today on the ubuntu-server mailing list to confirm the removal of the 32-bit (i386) daily ISO images of Ubuntu Server starting with Ubuntu 18.04 LTS.

Following in the footsteps of Ubuntu Desktop, the Ubuntu Server official flavor won't be shipping with 32-bit ISO images when the Ubuntu 18.04 LTS (Bionic Beaver) operating system will be released next year in April. Therefore, you won't be able to install Ubuntu 18.04 LTS as a server, nor desktop OS on an old 32-bit computer.