I know I'm not the only one here running older iron, so I'll share this
discovery.
The kernel delivered with the 32-bit 12.04 Beta-1 release does not support
non-PAE CPUs. As I understand it, that's the planned configuration for the
official release next month.
(PAE stands for "Physical Address Extension", a CPU feature that allows an OS to
exploit more than 4 GB of physical memory. It's a hardware feature of the CPU,
independent of whether you actually have more than 4 GB RAM or not.)
My Pentium 4 desktops are OK, even though they date from 2004. But my favorite
laptop (also from 2004) has a Pentium M Centrino CPU. That's not OK on 12.04.
It runs Unity 2D beautifully under 11.10; I'm even getting to like Unity a bit
for what I do on a laptop.
I'll admit to a certain level of annoyance here. There must be plenty of
laptops out there like mine, with more than enough horsepower to do what people
do while mobile. They're not ready for the scrap heap yet.
Time to go distro shopping. (Any recommendations?) Or learn how to compile a
kernel with non-PAE CPU support enabled.