The Itanium Architecture and What it Tries to Achieve

Itanium's architecture is explained here. But just for handy reference, here are the main highlights.

ia64 -

GOAL NUMERO UNO - is to support 64 bit addressing and 64 bit data types

Peformance and ease of use are obvious secondary goals. But also ease of interfacing with IA-32 is an important design goal.