title: What EXACTLY is the difference between intel's and amd's ISA, if any?
body: <p>I know people have asked similar questions like this before, however there is so much conflicting information that I really want to try and clear it up once and for all. I will attempt to do so by clearly distinguishing between instruction set architecture (ISA) and actual hardware implementation. First my attempted clarifications:</p>
  
  <p>1.) Currently there are intel64 and amd64 CPU's out there (among others but these are the focus)</p>
  
  <p>2.) Given that an ISA is the binary representation of 1 or more CPU instructions this means an ISA is completely separate from it's actual hardware implementation. </p>
  
  <p>My question(s):</p>
  
  <p>Does the differences between intel 64 and amd64 CPUs have to do with different or extended x86-64 ISAs? Or different hardware implementations of the x86-64 ISA? Or both?</p>