EM64T

From TPU Reference

EM64T is the instruction set that adds 64-bit support to Intel's line of processors(except the Itanium processors which uses the IA-64 instruction set). Intel now calls this instruction set Intel64, but most still refer to it as EM64T.

It is almost identical to AMD's AMD64 instruction set, however there are a few very minor differences. The two instruction sets are compatible, and most use the vendor neutral term x86-64 or x64 to refer to the two nearly identical implementations.