Itanium processors heralded a new era or processing. Though not very successful commercially, IPF has added many wonderful techniques to computer science. I'll discuss the one I liked the most.
It is called RSE (Register Stack Engine), a technique to avoid using main memory during function calls and do the stuff in processor register itself. When a function call is made, calling function passes the arguments that are saved in main memory. After this, the return address is saved. Main memory access is slower when compared to processor speed. Itanium has 128 GPR and out of those 96 are available for RSE. These 96 registers take care of function call mechanism, appearing as a register stack frame to the application. This bypasses memory access till all 96 registers are occupied. Interestingly, processor itself is responsible for running this show and also it's transparent to the application.
More here: http://software.intel.com/en-us/articles/itaniumr-processor-family-performance-advantages-register-stack-architecture