title: What does 'bank'ing a register mean?
body: <p>Reading 'ARM Architecture' on Wikipedia and found the following statement:</p>
  
  <blockquote>
    <p>Registers R0-R7 are the same across all CPU modes; they are never
    banked.</p>
    
    <p>R13 and R14 are banked across all privileged CPU modes except system
    mode.</p>
  </blockquote>
  
  <p>What does banking a register mean? </p>