How-to Install Ubuntu 12.x On Older Hardware
From version 12.x onward, many Ubuntu users thought they had hit the end of the line on their older hardware; the adoption of PAE kernels as standard without any non-PAE processor support put new versions beyond the Celeron and Pentium chips.
But you can install a version of 12.04 - remembering that's an LTS or Long Term Support release that has another two years life in it for software patches and updates.
Let's unwind that: Physical Address Extension (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. For that you need a PAE-supporting processor.
Ubuntu 12.04 and up uses the PAE Linux kernel by default on 32bit images, so old computers that don't support PAE can't boot this latest Ubuntu version. But there is a way to install Ubuntu 12.04 (Precise Pangolin) on computers without PAE support. One boot image, the non-PAE 'netboot' Minimal ISO uses the old kernel.
The non-PAE netboot mini ISO is a small 25Mb image that boots a non-PAE kernel, allowing you to install that and any officially supported desktop - or server - environment you want.
Since it is a minimal boot image, the text-based installer takes you very quickly into a boot menu with install options for server and desktop packages. You can choose to install the LAMP stack, DNS stack and other options: select to install the Ubuntu Unity Desktop Kubuntu KDE, LXDE and so on.
Be mindful that the minimal netboot CD contains next to nothing on the install CD itself; it downloads packages from online archives at install-time, so you need a working Internet connection during the installation.
You can download mini.iso, write it on a CD or USB stick and boot from it like with regular Ubuntu ISO and select "Install."
The text-based installer goes through the usual questions regarding the locale and time-zone, keyboard, and so on - the TAB key moves through fields on screen, SPACE bar selects the options and the ENTER key confirms each screen.
Like the regular Ubiquity installer, the mini ISO runs through country selection, encrypting your home directory, and partitioning the hard disk.
After partitioning the hard disk, the installer starts downloading the core packages. It will also ask you to select the Linux kernel you want to use - select "linux-generic."
For a desktop installation, make sure to select a desktop environment; skipping this will give you a core system without a graphical desktop environment, just a command line.
Finally, make sure you install the GRUB bootloader (selecting "Yes" when asked), otherwise it won't boot into Linux when you restart the machine.
I've used this method to update my ancient JVC-mini pre-netbook netbook with its' Celeron-M processor to non-PAE Ubuntu 12.04. With the LXDE desktop, effectively turning it into a Lubuntu machine.
I'm also using this method to perform my virtual server installs in virtualbox. It's so much easier than downloading the full 750Mb+ of standard disk images.
You can get the 12.04 Precise net-boot mini-ISO on this link and the 12.10 Quantal net-boot mini-ISO on this link. RC