64-Bit Ubuntu

Recent advances in computing saw the introduction of 64-bit x86-compatible CPUs from AMD in the spring of 2003. The only platform at launch to support the new technology was Linux, and even at the time of writing, it is still the only mainstream operating system actively using the power of the 64-bit x86 architecture. Intel's EM64T extensions for x86, which largely mirror the advances made by AMD, have further increased the availability of commodity x86-64 hardware.

Ubuntu fully supports AMD64 and Intel EM64T processors, and you are encouraged to use the 64-bit version of Ubuntu to get the maximum from these advanced processors.

As far as the Intel Itanium architecture goes, unfortunately Ubuntu does not currently support ia64. However, you may want to investigate Debian which is available for the ia64 platform.