Choose Ubuntu Mac 11.04 Amd64 Alternate CD to take full advantage of computers based on the AMD64 or EM64T architecture (e.g., Athlon64, Opteron, EM64T Xeon, Core 2). If you have a non-64-bit processor made by AMD, or if you need full support for 32-bit code, use the Intel x86 images instead. Ubuntu 11.04 is focused on home and mobile computing users, It introduces an array of online and off line applications to Ubuntu Desktop Edition with a particular focus on the personal cloud. It also includes a brand-new Ubuntu font family, a redesigned system installer, the latest GNOME 2.32 desktop, Shortwell as the new default photo manager, and a number of other features.
For almost all PCs. This includes most machines with Intel/AMD/etc type processors and almost all computers that run Microsoft Windows, as well as newer Apple Macintosh systems based on Intel processors.
About Ubuntu

Ubuntu is a complete desktop Linux operating system, freely available with both community and professional support. The Ubuntu community is built on the ideas enshrined in the Ubuntu Manifesto: that software should be available free of charge, that software tools should be usable by people in their local language and despite any disabilities, and that people should have the freedom to customise and alter their software in whatever way they see fit. "Ubuntu" is an ancient African word, meaning "humanity to others". The Ubuntu distribution brings the spirit of Ubuntu to the software world.