title: What is the purpose of SUB Instruction?
body: <p>I'm learning assembly on my own, I have a confusion that I would like to clear.</p>
  
  <p>So from what I understand a x86 computer uses the same circuit for addition and subtraction. For subtraction a negative number is converted to its 2 complement and then the addition circuit could be used to carry out the subtraction. Eg: The equation <code>4 - 2</code> is converted to <code>4 + (-2)</code></p>
  
  <p>So if subtraction can be done using the 2 complement then what is the purpose of the <code>SUB</code> Instruction?</p>