You are referring to the difference between the two server installer images:
Server install image for 64-bit PC (AMD64) computers (standard download) and
that also has versions for for different platforms: 64-bit ARM, PowerPC64 and IBM System z.
The difference is in the installers, and it's explained in BionicBeaver Release Notes:
The next generation Subiquity server installer, brings the comfortable
live session and speedy install of Ubuntu Desktop to server users at
N.B., If you require multipath, full-disk encryption, or the ability
to re-using existing partitions, you will want to continue to use the
alternate installer which can be downloaded from
As of 18.04.1, the Subiquity server installer now supports LVM, RAID, vlans, and bonds.
According to Ubuntu forums, there are also more differences between 18.04 "live" and "alternative":
Changing the hostname will revert back to the original name after reboot on an install using "live" unless the following is changed:
/etc/cloud/cloud.cfg and change
On a "live" install, the following mount exists:
/dev/loop0 88704 88704 0 100% /snap/core/4486
On the "live" install the settings for auto updates are in
/etc/apt/apt.conf.d/20auto-upgrades while on "alternative" install
they are in a different config file (just grep
The "live" install asks the user on the first login to install a language pack:
sudo apt-get install language-pack-en
cloud-init package is not installed by default with the "alternative" ISO but it is with the "live" ISO.