If you're reading this you probably tried to run a 12.04 live session or install 12.04 and were presented with this warning, "This kernel requires the following features not present on the CPU: pae. Unable to boot - please use a kernel appropriate for you CPU."
So what's up and what are your options?
In November 2011 the kernel devs seemed to have doomed the non-pae kernel but in December 2011 things began to look up, however when Precise Beta 1 was released the only real options to install a non-pae kernel were to upgrade from either Lucid or Oneiric or to use the netboot non-pae mini.iso.
But after some complaining on my part and requests from Xubuntu and Lubuntu the options have improved somewhat. Both the Xubuntu and Lubuntu 12.04 images now use the non-pae kernel by default. You should however consider that Lubuntu 12.04 is only supported for 18 months, and Xubuntu 12.04 is supported for 3 years, whereas Ubuntu 12.04 LTS itself is supported for 5 years.
The Ubuntu, Kubuntu, Edubuntu, and Mythbuntu i386 images all now use the PAE kernel by default but, as previously mentioned, upgrades from either 10.04 or 11.10 will remain non-pae. Please refer to the release notes or your distros official documentation regarding the proper upgrade methods and options.
And it's also quite possible to install 'ubuntu-desktop' on top of an Xubuntu or Lubuntu installation and still remain non-pae. Shortly after the final release of Precise I do plan on collaborating with the author of Psychocats on a full conversion method from either Xubuntu or Lubuntu to Ubuntu.
Remember when making a decision here that 12.04 is the end of the road for the non-pae kernel in Ubuntu so I'd personally think a 5 year LTS would be a good choice, but that's totally up to you, and the aforementioned non-pae mini.iso is a reasonable choice if you have a fast wired internet connection. You can read more about that in this forum post.
I should however also note that those with only wireless may (or may not) find that performing a CLI installation using an Lubuntu or Xubuntu alternate CD provides wireless modules not available on the mini.iso. To perform a CLI mode installation using an alternate CD you must press F4 and select CLI mode, then the rest of the installation is quite similar to performing a CLI install using the mini.iso.
There is now also an unofficial Ubuntu non-pae live image available here: