In-Stat's "Microprocessor Report" analyzed the instructions, memory-addressing schemes, and other features of the two architectures, and found in almost every case that Intel had patterned its after AMD64.

Intel clearly derived its 64-bit architecture by examining AMD's documentation for AMD64 and by testing AMD64 processors, said Tom Halfhill, a senior editor with In-Stat/MDR's "Microprocessor Report."

"Intel's reverse-engineering of AMD64 marks a major turning point in the historical relationship between the companies," said Halfhill in a statement. "Although AMD has in the past introduced some innovations to the x86 architecture, this is the first time AMD has truly steered the direction of the world's most important microprocessor architecture."

In-Stat's examination of the Intel and AMD 64-bit instruction sets found nothing to contradict Intel's claim that its 64-bit x86 processors will run 64-bit operating systems developed for AMD64, added Halfhill, but that minor differences do exist.

While those may make some software written for one chipset incompatible with the other, Halfhill was confident that the differences can be overcome.

Some may be resolved in future 64-bit x86 processors, he said, while in other instances, software can be written to first probe the CPU to find which 64-bit extensions it supports before running slightly different code.