How To Install Ubuntu 12.04 On Non-PAE Capable Hardware
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.
Ubuntu 12.04 (as well as Kubuntu 12.04 and newer Ubuntu versions) uses the PAE Linux kernel by default for 32bit ISOs so old computers that don't support PAE can't boot the latest Ubuntu version. But there is a way to install Ubuntu 12.04 LTS Precise Pangolin on computers without PAE support: using the non-PAE netboot Minimal ISO (there are also some alternatives, see below).
