From LXF Wiki
Itanium (often referred to as Itanic) is the name given to a range of CPUs developed by Intel. These 64-bit processors are a complete break from the x86 architecture, which has made them a hard sell to companies with large investments in the older architecture. That said, they do enable much more demanding applications to be run - particularly when it comes to using large amounts of memory. The Itanium and its successor, the Itanium 2, are often to be found in high-performance clusters, high-end servers and workstations.
The main competitor to the Itanium is AMD's Opteron.