I just noticed that the Kubuntu 12.04 LTS Beta1 DVD image
wont even boot on a Thinkpad T42p with Pentium M Dothan 400MHz FSB.
I looks like the Dothan CPU with 400MHz only is missing PAE support
PAE Wiki article

Bummer

As I learned from a reply in the kubuntu forums,
it is unlikely that Non-PAE system will be supported in 12.04 LTS.

https://lists.ubuntu.com/archives/ubuntu-devel/2011-November/034399.html

Just for completeness:
Non-PAE systems are officially supported via the Minimal CD or the upgrade path. (I have not tested this yet).
More complete info at Kubuntu Forums:
http://www.kubuntuforums.net/showthread.php?57669-12-04-Beta1-is-PAE-support-only

I first saw this issue when I tried to move an ubuntu 10.04 server virtual machine from the t43p to the t42p. VMware alerted that the VM used PAE instructions not present on the new host. I had to remake the machine with a non-PAE kernel before moving the VM. Unfortunately the T42 is the last generation that loses support for 32 bit machines driving more than 2 gigs of memory.

My feelings on Linux on the T42p (which I'm running at this moment) are that "age appropriate" distros work better than the latest stuff. Kubuntu 8.04 was the last to easily support ATI hardware acceleration which is much faster and suspends more reliably than the open source driver on the same hardware.

Anyway on other machines I'm a big fan of Kubuntu 11.10. It took almost forever for KDE 4 to restore all the features I really use from KDE 3 and to be able to configure the crashers and UI snafus out of kwin but I'm relieved Kubuntu has returned to excellence.

Thanks for the heads up.

Full ACK, Kubuntu 8.04 still rocks on my T42p.

^^ - But that's got little to nothing to do with the subject of this thread. And, besides, support ended for 8.04 almost a year ago.

Neil, only your post has nothing to do with getting Kubuntu to run perfectly on a T42p due to PAE now being compiled in by default.

Most Ubuntu users will be best served by the latest release or the latest LTS, but that's not necessarily true for the original topic poster, nor others with a machine from this era or before, despite the fact that old thinkpads always had perfect linux support.

Need T42p dual-head support? GFX acceleration? A kernel that works on the T42p? Ubuntu Hardy still works perfectly. Despite your FUD that it isn't supported, apt still has updates waiting for me this morning. Shhhh, nobody tell the people working on updates or the servers supplying them that they no longer exist. You know what doesn't exist? Kubuntu 12.04, or Kubuntu 12.10 for that matter.

The core of the problem is that PAE kills support for most 32 bit systems and only benefits people who would be better served by a 64 bit kernel. The 32 bit ubuntu releases work perfectly on 64 bit systems, but they're not going to work on most 32 bit systems out of the box.

cheers to lophiomys for good info
the clueless will be ignored or corrected!

Actually, his "FUD" is correct, just incomplete. Support and updates for Hardy on the desktop is, indeed, done. Server packages will receive support/updates until April 2013.

So yeah, there may still be updates waiting for you, but not for desktop packages. And since we're talking about what distro to use for a desktop/laptop system, I don't think it's unfair to say that this is an important consideration.