Both Intel and AMD have FREE documentation for their processors available on their websites.
Intels IA64 (Itanium) Instruction set reference is available here
http://www.intel.com/design/itanium/manuals/245319.htm
I couldnt find the AMD docs for the X64 Instruction set, but you can try searching from developer.amd.com.
Steve Wort
Co Author "Professional SQL Server 2005 Administration"