When I tried to install Ubuntu 12.04 on an old ThinkPad X40 I was surprised to discover this warning on my screen:
This kernel requires the following features not present on the CPU: pae. Unable to boot - please use a kernel appropriate for your CPU.
In few words I wasn’t able to install Ubuntu 12.04 because the kernel on Ubuntu 12.04 was not supporting my CPU and I was really upset because I have always promoted Linux distributions as the most versatile and appropriate OS to keep using “old” hardware.
Sincerely, as described in an older post, I previously decided to install MATE desktop environment because the graphic cards on many laptops didn’t support Unity and Gnome 3 but this was the first time I had to renounce the installation of Ubuntu. I didn’t want to surrender to this difficulty (that appeared to me as a bug)!
First of all, I discovered that pae is “a feature to allow 32-bit x86 processors to access a physical address space (including random access memory and memory mapped devices) larger than 4 gigabytes“. After I clarified this point, I was not sure that my processor was totally inadequate to support Ubuntu 12.04.
After some web surfing I discovery that there are two easy solutions to avoid this problem.
More in general, it is also possible to assume that if you have a non PAE CPU, your hardware could not be able to support the Unity desktop. For this reason you can keep your Lubuntu – Xubuntu (based on the light but effective LXDE desktop) or switch your desktop environment to Gnome (the Classic, of course) installing the gnome package instead of ubuntu-desktop.
In any case, if you want to know if your CPU supports pae you have to open a Terminal and type:
grep --color=always -i PAE /proc/cpuinfo