EM64T & x86_64 only exist because Intel has too much pride to call it what it is: AMD64.
I, myself, had an AMD Opteron machine on which I ran an x86-64 build, with that name for the architecture, of SUSE Linux before Intel released their EM64T.
http://www.amd.com/us/press-releases/Pages/Press_Release_715...
Dated 8/10/2000.