title: What is the difference between concrete RTN and abstract RTN?
body: <p>I have been reading about RTN (Register Transfer Notation) and I have come upon abstract RTN. There is no explanation about the difference between concrete RTN and  abstract RTN. </p>
  
  <p>Could anyone explain to me the difference between the two both in how you write the code and how it interacts with the machine? </p>