Back during the Ubuntu 12.04 LTS Developer Summit in Orlando, the developers decided they wanted to drop non-PAE kernel support. For 32-bit Linux the PAE kernel allows addressing more than 4GB of system memory, while the kernel without support for PAE isn't. Most hardware that's only 32-bit capable (if your hardware is x86_64 compatible you should be using the 64-bit build by now, really) does have support for Physical Address Extensions, so Ubuntu developer wants to get rid of this extra non-PAE kernel.
Well, many were concerned by Ubuntu dropping non-PAE kernel support. There's still some Intel Pentium M CPUs that were made in the past decade that lacked PAE support, among other reasons people still wanted to see non-PAE kernel support in this next Ubuntu Long Term Support release.
The Ubuntu Technical Board weighed the pros and cons of non-PAE support and came to a decision. The board has decided they will support the non-PAE kernel option until the Ubuntu 12.10 release, so there will still be support in Ubuntu 12.04 LTS. The default i386 kernel in Ubuntu 12.04 LTS will become the PAE-enabled kernel, but the non-PAE flavor will be available.
Below are the details in full from the non-PAE discussion.
Non-PAE kernel disposition
* Kernel team would like to drop non-PAE kernel soon
* TB members generally feel that (1) dropping the current default kernel is too much of a step, and (2) there is still a significant number of users which have non-PAE systems, based on Launchpad bug report data and an ubuntu-devel@ strawpoll
* Maintaining the extra flavour is not much extra work, and not comparable to e. g. the -ti-omap4 kernel which is an entirely separate source tree
* We need a way to prevent upgrades for non-PAE systems. Some options were mentioned:
* Add update-manager check to not offer the upgrade if PAE is not available
* Add libc6/linux preinst to abort the upgrade early if PAE is not available; that's not the best failure mode, but will prevent a safety net for users of `apt-get dist-upgrade`
* Switch precise over to PAE kernel by default on i386; we retain the option to revert if it causes too much fallout (Colin)
* Drop non-PAE flavour in 12.10; this will give non-PAE systems another 5 years of life time, which is considered enough
* Further discuss upgrade strategy/checks
Now see i686 vs. i686 PAE vs. x86_64 Linux benchmarks from April.