title: Memory Hierarchy - Why are registers expensive?
body: <p>I understand that:</p>
  
  <p><strong>Faster</strong> access time > <strong>More</strong> expensive</p>
  
  <p><strong>Slower</strong> access time > <strong>Less</strong> expensive</p>
  
  <p>I also understand that registers are the top of the hierarchy, and have the fastest access time. What I am having a hard time researching is <em>why</em> it's so expensive? To my knowledge, registers are literally circuits built directly into the ALU. If they're literally built into the CPU (the ALU especially), what actually makes it the most expensive?</p>
  
  <p>Is it the size (registers being the smallest, of course)?</p>